Computer virus

Domain Seminar Report on
Computer Viruses
Submitted by:
B.Tech (CSE/IT) II Semester
Under the Guidance of
Amity School of Engineering and Technology
AMITY UNIVERSITY RAJASTHAN

Declaration
I hereby declare that the report entitled Computer Viruses submitted for the
partial fulfilment of B.Tech degree is my original work and the report has not
formed the basis for the award of any degree, associate ship, fellowship or any
other similar titles.
Counter Signature of the Guide:
Name of the Guide :
Designation:
Date:

Acknowledgements
First of all, I would like to sincerely thank my supervisor, , for his persistent support,
guidance, help, and encouragement during the whole process of my study.
Moreover, I would like to thank our Director- ASET and Dr. Tarun Kumar Sharma, HOD,
CSE who were always there whenever we needed any support.
I would also like to thank my parents for their well wishes to complete this work. Finally
thanks to all friends for their support.
Contents

Abstract Pg.No.1
List of Figures and Tables Pg.No.2
1 Introduction Pg.No.3
1.1 What are the Computer viruses? Pg.No.3
1.2
adsa
d
How do Computer viruses attack? Pg.No.4
1.3 How do Computer viruses spread? Pg.No.4
1.4 What are the signs of Computer viruses? Pg.No.5
1.5 What are the different types of Computer virus? Pg.No.5
2 CategoriesofComputer viruses Pg.No.7
2.1 Worms Pg.No.7
2.2 Trojan Pg.No.8
2.3 Adware Pg.No.9
2.4 Rootkit Pg.No.10
2.5 Ransomware Pg.No.12
3 Virus Histroy Pg.No.16
3.1 Before the Virus Pg.No.16
3.2 Initial era Pg.No.16
3.3 The Document Virus Pg.No.17
4 Impact on IT system Pg.No.18
4.1 Intro Pg.No.18
4.1.1 Harmless effect Pg.No.18
4.1.2 Compatibility problem Pg.No.18
4.1.3 Compromise system integrity Pg.No.18
4.1.4 Granting un-authorised access Pg.No.19
4.1.5 Discloser of confidential data Pg.No.19
4.1.6 Computer resource usage Pg.No.19
4.1.7 Human resource usage Pg.No.19
4.1.8 PR aspects Pg.No.20
References Pg.No.21

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Abstract
A virus is a small piece of software that piggybacks on real programs in order to get
executed. Once it’s running, it spreads by inserting copies of itself into other executable code
or documents. A piece of code which is capable of copying itself and typically has a
detrimental effect, such as corrupting the system or destroying data. Computer viruses
currently cause billions of dollars' worth of economic damage each year, due to causing
system failure, wasting computer resources, corrupting data, increasing maintenance costs,
etc. In response, free antivirus tools have been developed, and an industry of antivirus
software has cropped up, selling or freely distributing virus protection to users of
various operating systems. As of 2005, even though no currently existing antivirus software
was able to uncover all computer viruses (especially new ones), computer security
researchers are actively searching for new ways to enable antivirus solutions to more
effectively detect emerging viruses, before they have already become widely distributed.

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List of Figures and Tables
Figure 1 Virus detected by Computer Pg.No.3
Figure 2 Virus spreading Pg.No.4
Figure 3 Hex dump of the worm Pg.No.7
Figure 4 Example of Adware and pop-ups Pg.No.10
Figure 5 Working of Rootkits Pg.No.11
Figure 6 Paying Ransomware Pg.No.12
Figure 6 Reveton Pg.No.15

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Chapter - 1
Introduction
1.1 What are Computer Viruses ?
A computer virus, much like a flu virus, is designed to spread from host to host and has the
ability to replicate itself. Similarly, in the same way that flu viruses cannot reproduce without
a host cell, computer viruses cannot reproduce and spread without programming such as a file
or document.
In more technical terms, a computer virus is a type of malicious code or program written to
alter the way a computer operates and is designed to spread from one computer to another. A
virus operates by inserting or attaching itself to a legitimate program or document that
supports macros in order to execute its code. In the process, a virus has the potential to cause
unexpected or damaging effects, such as harming the system software by corrupting or
destroying data.
Figure 1 : Virus detected by Computer

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1.2 How the Computer Virus attack?
Once a virus has successfully attached to a program, file, or document, the virus will lie
dormant until circumstances cause the computer or device to execute its code. In order for a
virus to infect your computer, you have to run the infected program, which in turn causes the
virus code to be executed.
This means that a virus can remain dormant on your computer, without showing major signs
or symptoms. However, once the virus infects your computer, the virus can infect other
computers on the same network. Stealing passwords or data, logging keystrokes, corrupting
files, spamming your email contacts, and even taking over your machine are just some of the
devastating and irritating things a virus can do.
While some viruses can be playful in intent and effect, others can have profound and
damaging effects. This includes erasing data or causing permanent damage to your hard disk.
Worse yet, some viruses are designed with financial gains in mind.
Figure 2 : Virus spreading
1.3 How do Computer Viruses spread?
In a constantly connected world, you can contract a computer virus in many ways, some more
obvious than others. Viruses can be spread through email and text message attachments,
Internet file downloads, and social media scam links. Your mobile devices and smartphones
can become infected with mobile viruses through shady app downloads. Viruses can hide
disguised as attachments of socially shareable content such as funny images, greeting cards,
or audio and video files.

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To avoid contact with a virus, it’s important to exercise caution when surfing the web,
downloading files, and opening links or attachments. To help stay safe, never download text
or email attachments that you’re not expecting, or files from websites you don’t trust.
They are usually downloaded by the sites which provided free games and torrent sites. Most
users download application which are not paid but reality they are paid on their own company
sites.
1.4 What are the signs of Computer Virus?
A computer virus attack can produce a variety of symptoms. Here are some of them:
 Frequent pop-up windows. Pop-ups might encourage you to visit unusual sites. Or
they might prod you to download antivirus or other software programs.
 Changes to your homepage. Your usual homepage may change to another website,
for instance. Plus, you may be unable to reset it.
 Mass emails being sent from your email account. A criminal may take control of
your account or send emails in your name from another infected computer.
 Frequent crashes. A virus can inflict major damage on your hard drive. This may
cause your device to freeze or crash. It may also prevent your device from coming
back on.
 Unusually slow computer performance. A sudden change of processing speed could
signal that your computer has a virus.
 Unknown programs that start up when you turn on your computer. You may
become aware of the unfamiliar program when you start your computer. Or you might
notice it by checking your computer’s list of active applications.
 Unusual activities like password changes. This could prevent you from logging into
your computer.
1.5 What are the difference types of Computer Virus?
1. Boot sector virus
This type of virus can take control when you start — or boot — your computer. One
way it can spread is by plugging an infected USB drive into your computer.
2. Web scripting virus
This type of virus exploits the code of web browsers and web pages. If you access
such a web page, the virus can infect your computer.
3. Browser hijacker

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This type of virus “hijacks” certain web browser functions, and you may be
automatically directed to an unintended website.
4. Resident virus
This is a general term for any virus that inserts itself in a computer system’s memory.
A resident virus can execute anytime when an operating system loads.
5. Direct action virus
This type of virus comes into action when you execute a file containing a virus.
Otherwise, it remains dormant.
6. Polymorphic virus
A polymorphic virus changes its code each time an infected file is executed. It does
this to evade antivirus programs.
7. File infector virus
This common virus inserts malicious code into executable files — files used to
perform certain functions or operations on a system.
8. Multipartite virus
This kind of virus infects and spreads in multiple ways. It can infect both program
files and system sectors.
9. Macro virus
Macro viruses are written in the same macro language used for software applications.
Such viruses spread when you open an infected document, often through email
attachments.

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Chapter -2
Categories of Virus
2.1 Worms
Worm is a self-replicating program, similar to a computer virus. A virus attaches itself to,
and becomes part of, another executable program; however, a worm is self-contained and
does not need to be part of another program to propagate. Worm is a small piece of
software that uses computer networks and security holes to replicate itself. A copy of the
worm scans the network for another machine that has a specific security hole. It copies
itself to the new machine using the security hole, and then starts replicating from there, as
well.
Figure 3 – Hex dump of the worm, showing a message left for Microsoft CEO Bill Gates by
the worm programmer Blaster [2]
Worms spread by exploiting vulnerabilities in operating systems. Vendors with security
problems supply regular security updates (see "Patch Tuesday"), and if these are installed
to a machine then the majority of worms are unable to spread to it. If a vulnerability is
disclosed before the security patch released by the vendor, a zero-day attack is possible.
Like the ILOVEYOU virus, which destroyed the files of more than 50 million internet
users worldwide, rendered PCs unbootable, copied people’s passwords and sent them to
its creators, and caused up to US$9 billion in damages in the year 2000.

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2.2 Trojans
A Trojan horse, or Trojan, is any malware which misleads users of its true intent. The term
is derived from the Ancient Greek story of the deceptive wooden horse that led to the fall of
the city of Troy.
Trojans are generally spread by some form of social engineering, for example where a user is
duped into executing an e-mail attachment disguised to appear not suspicious, (e.g., a routine
form to be filled in), or by clicking on some fake advertisement on social media or anywhere
else. Although their payload can be anything, many modern forms act as a backdoor,
contacting a controller which can then have unauthorized access to the affected
computer. Trojans may allow an attacker to access users' personal information such as
banking information, passwords, or personal identity. It can also delete a user's files or infect
other devices connected to the network. Ransomware attacks are often carried out using a
Trojan.
Unlike computer viruses and worms, Trojans generally do not attempt to inject themselves
into other files or otherwise propagate themselves.
This is normally done by social engineering -- the author of the Trojan horse has to convince
you to download the application. Alternately, he or she might send the program to you in
an e-mail message hoping you execute it. Again, this is why it is called a Trojan horse -- you
have to consciously or unconsciously run the .exe file to install the program -- it doesn't
propagate on its own like a virus (see How Computer Viruses Work for a description of
Trojans and viruses). Once you execute the program, the Trojan server is installed and will
start running automatically every time you power up your computer.
The most common way Trojan horses spread is through e-mail attachments. The developers
of these applications typically use spamming techniques to send out hundreds or even
thousands of e-mails to unsuspecting people; those who open the messages and download the
attachment end up having their systems infected.
Crackers -- hackers who use their computer skills to create mischief or cause damage
intentionally -- can send out Trojans that turn innocent Web surfer's computers into zombie
computers, so-called because the person with the infected computer rarely knows his system
is under control. Crackers then use these zombie computers to send out more viruses,
eventually creating networks of zombie computers known as botnets.
Trojan in this way may require interaction with a malicious controller (not necessarily
distributing the Trojan) to fulfill their purpose. It is possible for those involved with Trojans
to scan computers on a network to locate any with a Trojan installed, which the hacker can
then control.
Some Trojans take advantage of a security flaw in older versions of Internet Explorer and
Google Chrome to use the host computer as an anonymizer proxy to effectively hide Internet
usage, enabling the controller to use the Internet for illegal purposes while all potentially
incriminating evidence indicates the infected computer or its IP address. The host's computer

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may or may not show the internet history of the sites viewed using the computer as a proxy.
The first generation of anonymizer Trojan horses tended to leave their tracks in the page
view histories of the host computer. Later generations of the Trojan tend to "cover" their
tracks more efficiently. Several versions of Sub7 have been widely circulated in the US and
Europe and became the most widely distributed examples of this type of Trojan.
2.3 Adware
Adware, or advertising-supported software, is software that generates revenue for its
developer by automatically generating online advertisements in the user interface of the
software or on a screen presented to the user during the installation process. The software
may generate two types of revenue: one is for the display of the advertisement and another on
a "pay-per-click" basis, if the user clicks on the advertisement. The software may implement
advertisements in a variety of ways, including a static box display, a banner display, full
screen, a video, pop-up ad or in some other form.
Adware is categorized as follows:
 Legitimate: Free or trial product sponsored advertisements
 Spyware: Tracks user website preferences and compromises privacy
Adware may appear innocuous and provide users with legitimate business software but then
unleash spyware that collects browser search data for targeted user-specific advertisements.
Uninstalling adware generally requires anti-adware software. A variety of free and paid
versions are available, but licensed adware is the most reliable, aggressive and recommended.
Anti-adware software is also included in virus scanning packages.
Application software
Some software is offered in both an advertising-supported mode and a paid, advertisement-
free mode. The latter is usually available by an online purchase of a license or registration
code for the software that unlocks the mode, or the purchase and download of a separate
version of the software.
Some software authors offer advertising-supported versions of their software as an alternative
option to business organizations seeking to avoid paying large sums for software licenses,
funding the development of the software with higher fees for advertisers.
Software as a service
Support by advertising is a popular business model of software as a service (SaaS) on
the Web. Notable examples include the email service Gmail and other Google Apps (now G
Suite) products, and the social network Facebook. Microsoft has also adopted the advertising-
supported model for many of its social software SaaS offerings. The Microsoft Office
Live service was also available in an advertising-supported mode.

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Figure 4 – Example of Adware and pop-ups
2.4 Rootkits
A rootkit is software used by a hacker to gain constant administrator-level access to a
computer or network. A rootkit is typically installed through a stolen password or by
exploiting a system vulnerabilities without the victim's consent or knowledge.
Rootkits primarily aim at user-mode applications, but they also focus on a computer’s
hypervisor, the kernel, or even firmware. Rootkits can completely deactivate or destroy the
anti-malware software installed in an infected computer, thus making a rootkit attack difficult
to track and eliminate. When done well, the intrusion can be carefully concealed so that even
system administrators are unaware of it.

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Figure 5 – Working of Rootkits
Rootkits may be also presented as a Trojan or even as a hidden file along with a seemingly
harmless file. This can be a graphic or even a silly application distributed via email. When the
victim clicks the program or graphic, the rootkits are installed on their system without their
knowledge.
Some of the impacts of rootkits are often to:
 Provide the attacker with complete backdoor access, permitting them to falsify or
steal documents.
 Hide other malware, especially keyloggers. The keyloggers may then be used to
access and steal the victim's sensitive data.
 Enable the attacker to use the infected machine as a zombie computer to trigger
attacks on others.

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2.5 Ransomware
Ransomware is a subset of malware in which the data on a victim's computer is locked,
typically by encryption, and payment is demanded before the ransomed data is decrypted and
access is returned to the victim. The motive for ransomware attacks is nearly always
monetary, and unlike other types of attacks, the victim is usually notified that an exploit has
occurred and is given instructions for how to recover from the attack. Payment is often
demanded in a virtual currency, such as Bitcoin, so that the cybercriminal's identity is not
known. Ransomware malware can be spread through malicious email attachments, infected
software apps, infected external storage devices and compromised websites. Attacks have
also used remote desktop protocol and other approaches that do not rely on any form of user
interaction.
Figure 6 – WannaCry
Ransomware attacks are typically carried out using a Trojan that is disguised as a legitimate
file that the user is tricked into downloading or opening when it arrives as an email
attachment. However, one high-profile example, the "WannaCry worm", traveled
automatically between computers without user interaction.
Ransomware kits on the deep web have allowed cybercriminals to purchase and use a
software tool to create ransomware with specific capabilities. They can then generate this
malware for their own distribution and with ransoms paid to their bitcoin accounts. As with

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much of the rest of the IT world, it is now possible for those with little or no technical
background to order up inexpensive ransomware as a service (RaaS) and launch attacks with
minimal effort. In one RaaS scenario, the provider collects the ransom payments and takes a
percentage before distributing the proceeds to the service user.
Figure 6 – Paying Ransomware
Types of ransomware
Attackers may use one of several different approaches to extort digital currency from their
victims. For example:
 Ransomware known as scareware will try and pose as security software or tech support.
Victims may receive pop-up notifications saying malware has been discovered on their
system (which, an un-owned security software would not have access to this
information). Not responding to this will not do anything except lead to more pop-ups.
 Screen lockers, or lockers, are a type of ransomware designed to completely lock a user
out of their computer. Upon starting up the computer a victim may then see what looks to
be an official government seal, leading the victim into believing they are the subject of an
official inquiry. After being informed that unlicensed software or illegal web content has
been found on their computer, the victim is given instructions for how to pay an
electronic fine. However, official government organizations would not do this; they
instead would go through proper legal channels and procedures.

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 In encrypting ransomware, or data kidnapping attacks, the attacker will gain access to and
encrypt the victim’s data and ask for a payment to unlock the files. Once this happens,
there is no guarantee that the victim will get access to their data back- even if they
negotiate for it.
 Similar to encrypting ransomware, the attacker may also encrypt files on infected devices
and will make money by selling a product that promises to help the victim unlock files
and prevent future malware attacks.
 In doxware, an attacker may also threaten to publish your data online if the victim does
not pay a ransom.
 Mobile ransomware is ransomware which affects mobile devices. An attacker can use
mobile ransomware to steal data from a phone or lock it and require a ransom to return
the data or unlock the device.
 The victim may also receive a pop-up message or email ransom note warning that if the
demanded sum is not paid by a specific date, the private key required to unlock the device
or decrypt files will be destroyed.
WannaCry
In May 2017, the WannaCry ransomware attack spread through the Internet, using an exploit
vector named EternalBlue, which was leaked from the U.S. National Security Agency. The
ransomware attack, unprecedented in scale, infected more than 230,000 computers in over
150 countries, using 20 different languages to demand money from users
using Bitcoin cryptocurrency. WannaCry demanded US$300 per computer. The attack
affected Telefonica and several other large companies in Spain, as well as parts of the
British National Health Service (NHS), where at least 16 hospitals had to turn away patients
or cancel scheduled operations, FedEx, Deutsche Bahn, Honda, Renault, as well as
the Russian Interior Ministry and Russian telecom MegaFon. The attackers gave their victims
a 7-day deadline from the day their computers got infected, after which the encrypted files
would be deleted.
CryptoLocker
Encrypting ransomware reappeared in September 2013 with a Trojan known
as CryptoLocker, which generated a 2048-bit RSA key pair and uploaded in turn to a
command-and-control server, and used to encrypt files using a whitelist of specific file
extensions. The malware threatened to delete the private key if a payment of Bitcoin or a pre-
paid cash voucher was not made within 3 days of the infection. Due to the extremely large
key size it uses, analysts and those affected by the Trojan considered CryptoLocker extremely
difficult to repair. Even after the deadline passed, the private key could still be obtained using
an online tool, but the price would increase to 10 BTC—which cost approximately US$2300
as of November 2013.
CryptoLocker was isolated by the seizure of the Gameover ZeuS botnet as part of Operation
Tovar, as officially announced by the U.S. Department of Justice on 2 June 2014. The

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Department of Justice also publicly issued an indictment against the Russian hacker Evgeniy
Bogachev for his alleged involvement in the botnet. It was estimated that at least US$3
million was extorted with the malware before the shutdown.
Reveton
In 2012, a major ransomware Trojan known as Reveton began to spread. Based on the
Citadel Trojan (which itself, is based on the ZeusTrojan), its payload displays a warning
purportedly from a law enforcement agency claiming that the computer has been used for
illegal activities, such as downloading unlicensed software or child pornography. Due to this
behaviour, it is commonly referred to as the "Police Trojan". The warning informs the user
that to unlock their system, they would have to pay a fine using a voucher from an
anonymous prepaid cash service such as Ukash or paysafecard. To increase the illusion that
the computer is being tracked by law enforcement, the screen also displays the computer's IP
address, while some versions display footage from a victim's webcam to give the illusion that
the user is being recorded.
Figure 6 – Reveton
Reveton initially began spreading in various European countries in early 2012.[5] Variants
were localized with templates branded with the logos of different law enforcement
organizations based on the user's country; for example, variants used in the United Kingdom
contained the branding of organizations such as the Metropolitan Police Service and
the Police National E-Crime Unit. Another version contained the logo of the royalty
collection society PRS for Music, which specifically accused the user of illegally
downloading music. In a statement warning the public about the malware, the Metropolitan
Police clarified that they would never lock a computer in such a way as part of an
investigation.

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In May 2012, Trend Micro threat researchers discovered templates for variations for
the United States and Canada, suggesting that its authors may have been planning to target
users in North America. By August 2012, a new variant of Reveton began to spread in the
United States, claiming to require the payment of a $200 fine to the FBI using
a MoneyPak card. In February 2013, a Russian citizen was arrested in Dubai by Spanish
authorities for his connection to a crime ring that had been using Reveton; ten other
individuals were arrested on money laundering charges. In August 2014, Avast
Software reported that it had found new variants of Reveton that also distribute password-
stealing malware as part of its payload.

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Chapter - 3
Virus History
3.1. Before the viruses
UNIX worms and academic papers 1970 – 1988. Viruses are not a new invention. The idea
of self-replicating computer programs has been around for decades. This idea has emerged
in science fiction literature, scientific papers and even experiments at least since the early
1970s. Some attempts to perform maintenance tasks in large networks using worms were
made, but this technology did not become widespread or well known. One of the
milestones in virus history was the research performed by Dir. Fred Cohen in the early
1980s. Cohen formed the original definition of a virus; a program that can infect other
programs by modifying them to include a copy of itself. Cohen’s work was truly ground
breaking as it was published before the first viruses were ever made. In the 1980s the
Internet was a network that connected university computers to each other. This network
was pretty vulnerable to pure worms, which was to be demonstrated by a young student
named Robert Morris. The first major malware incident was probably the Morris worm in
November 1988. This UNIX-based worm knocked out almost all computers on the Internet,
causing a lot of media interest and many headlines.
3.2. The initial era
Standalone computers and LANs 1987 – 1990. The first PCs were made in the early 1980s.
The personal computer concept was new and revolutionary, and its popularity grew faster
than anyone expected. PCs were already a usable and affordable technology for companies in
the late 1980s. The rapid growth also brought computer technology closer to a larger number
of individuals. Several early viruses were made around 1987 – 1988, at least partly inspired
by Cohen’s work. Lehigh2 , Jerusalem3 and Brain4 are examples of the earliest viruses. Boot
sector viruses were the first type of virus to become common. Floppy diskettes were the only
way to transfer data from one PC to another so it is natural that the first viruses used this
media to replicate. The other basic type of virus, traditional file viruses, also started to
become more common at this time.
1990 – 1995 Local area networks began to appear in business environments. This
development gave the traditional file viruses a small advantage compared to boot sector
viruses. However, both groups were still common. The virus problem was not very well
known at this time. Many computer users were able to work for several years without
encountering a virus. Finding a virus was a rare event and some users collected the samples

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they found. Some viruses did, however, cause damage and business users started to become
aware of the problem. The boot sector virus Form5 became the most widespread virus during
this period. Another well-known virus of this era was Dark Avenger, also known as Eddie6 ,
and which was a very destructive virus.
3.3. The document viruses
Towards a major problem 1995 – 1998. From 1995, local area networks are already standard
equipment in most companies using personal computers. Internet connections also started to
become popular, especially in larger companies. The concept of email had been known in the
UNIX world for decades, but now this technology entered PC based corporate networks as
well. The presence of a local area network and Internet connectivity opened totally new ways
to communicate. The LAN was not just a way to share disks and printers anymore. Email had
become a significant communication channel, especially in large multinational companies.
The new technology introduced by email and the Internet revolutionized the way to work
with personal computers. But the existing viruses were not able to benefit from the new
technology. The number of boot sector virus infections started to decline when LANs, email
and CD-ROMs made floppies obsolete. File viruses did not benefit either as email was rarely
used for sending program files. The first macro virus, WM/Concept7 , was discovered in
August 1995. This virus was clearly a proof-of-concept virus, as the name also indicates. The
virus contained a routine called “Payload” but the only line in this routine was “This should
be enough to prove my point”. It soon became clear that this new category of viruses, one
that infected document files, was spreading quickly. An infected document could be
transmitted to a large number of users in minutes. More and more of a company’s IT support
resources were used for cleaning up virus infections. Viruses were not a funny joke anymore;
they had become a real problem especially for large companies. Some of the common viruses
at this time were WM/Cap8 and XM/Laroux9 .

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Chapter 4
Impact on IT systems
4.1 Intro
The damage caused by viruses and worms can be divided into two categories: intentional
damage and unintentional damage. Intentional damage, or harmless effects, is caused
explicitly by the payload routine. Unintentional damage may be caused as a side effect when
the virus replicates. It is a common misconception that all viruses are malicious by nature. As
a matter of fact, many common viruses lack a payload altogether. It is natural that a virus that
does not harm its hosts spreads much more efficiently than a destructive virus. The virus is
dependent on the host and harming it also reduces the virus’ chances to replicate. The term
harmless virus is sometimes used to describe a virus that lacks a payload routine, or has a
payload routine that only contains non-malicious effects. However, this term is misleading as
most viruses are likely to cause some kind of unintentional damage. Several of the groups
listed here apply to all viruses, especially the unintentional PR damages and IT support
workload. Many viruses also contain a single or multiple intentional effects.
4.1.1 Harmless effects
These effects are always produced by the payload routine, but they are not malicious. The
effect may be a picture, animations or video, music or sounds, interactive functions, political
messages etc. These effects usually give you an idea about the virus author’s way of thinking,
age or nationality. These effects may be funny or annoying and may distract or disturb the
user, but they do not cause any permanent damage.
4.1.2 Compatibility problems
Individuals make viruses and worms and they do not have resources to test their creations on
a wide range of computer systems. Nor do they develop the viruses according to quality
control systems and guidelines. This makes it likely that they cause compatibility problems
when run on systems that differ from the one on which they were developed. These problems
can occur as error messages, crashes, inability to access certain functions etc. These problems
are grouped as unintentional damage.
4.1.3 Compromising system Integrity
Intentional damage is often caused by erasure or modification of data. Erasing files is perhaps
the most obvious way to cause damage. Erasing files, however, is a clumsy way and modern,
well maintained, systems can usually recover from backups. Modifying data is a much more
sophisticated strategy. Small changes are made to the system now and then. The backup
routine stores partially corrupted data until the virus is detected. Restoring the data is hard or
impossible as several generations of backups are compromised. The last correct backups may
be too old and it may even be hard to tell which backups are or are not valid. High-level
viruses, such as macro viruses, do not have to operate on binary data as previous viruses did.
The macro languages provide powerful functions for modifying data in documents. This
enables viruses to perform sinister modifications that are critical but hard to detect. For

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example, it is possible for a macro virus to alter the text of a document before printing, but
show the correct form on screen. Usage of corrupted data may lead to severe damage. An
Excel sheet may, for example, be used to calculate the amount of concrete needed for a
bridge, or calculate how much fuel a jumbo jet needs to cross the Pacific.
4.1.4 Granting unauthorized access
Viruses may plant backdoors in the system, or steal passwords. These functions can later be
used by hackers to access the system. Damage caused by such hacking activities is hard to
predict. Unauthorized usage of the system may, for example, continue unnoticed for a long
time.
4.1.5 Disclosure of confidential data
Viruses and worms have access to the same communication methods as the user, and even
use them to replicate. A payload routine may easily locate documents that match certain
criteria and send them to anyone on the Internet. Some email worms also cause disclosure of
data as a part of replication. The worms that replicate when attached to a document, such as
Melissa, send this document to recipients to whom the user had no intention of sending the
document. The following example illustrates this. A company asks for offers from several
vendors. One of the vendors is infected with Melissa. The offer is mailed to the buyer as a
document infected with Melissa. The buyer opens the document and becomes infected
immediately. The Melissa worm examines the address book and send itself to the first 50
addresses on the list. The document that is sent is the offer from the infected vendor, and the
list of recipients probably contains the competitors.
4.1.6 Computer resource usage
Viruses and worms can disturb computer systems by spending resources, either intentionally
or unintentionally. Some viruses contain payloads that deliberately eat system resources, but
resource consumption is probably unintentional in most cases. Unintentional resource
consumption may be caused by errors in the virus or the replication. Code Red is an example
of this. Searching for new hosts to spread to requires both network traffic and CPU resources.
This load was obvious in the slower response time from the infected web servers or even in
the total inability to serve users. Another type of intentional resource usage is known as
denial-of-service or DOS. This is typically performed using distributed technology where a
large number of computers run so-called ‘zombies’. All these zombies are programmed to
connect to the same computer simultaneously. This does not significantly harm the systems
that run the zombies, but the target system is usually blocked due to an overloaded Internet
connection.
4.1.7 Human resource usage
Cleaning virus infections means extra work for the IT support staff. This damage, and the
downtime for the user, may result in great expense unless the viruses are stopped properly
using anti-virus software. Even if viruses are successfully stopped using anti-virus software,
the cost of maintaining this system may be seen as a cost caused by viruses.

21
4.1.8 PR aspects
The attitude towards viruses is negative. The problem is well known and all business users
know the severity. Sending a virus to a customer or business partner is not good for the
company’s image. This may be especially dangerous if the incident makes it to the headlines.
This is not at all impossible, especially if the virus was included in a mass-produced software
product.

22
Conclusion
Adapting to new architectures. The computer systems used by business and home users have
developed tremendously over the past ten years. Both system architecture and the way we use
computers is totally different from the late 1980s and early 1990s. But the virus problem is
still there, worse than ever. As a matter of fact, viruses and worms have been able to adopt
and benefit from the new features that modern computer environments offer. Virus strains do
not evolve as they spread. Some argue that viruses are primitive computer-based life forms,
but they certainly lack one of the fundamental capabilities of living creatures: to produce
descendants that are slightly more adapted to a new environment than their parents. This
means that as viruses cannot adapt to new system architectures, they become extinct when the
number of suitable host systems decreases. New strains are always created by a human, never
through natural evolution. However, the whole virus problem does adapt to new architectures
and benefit from them. New viruses are written as old ones become extinct. This means that
there are always new viruses that take advantage of the latest computer architectures. There
are always some viruses or worms that are able to efficiently use the latest and most powerful
ways to communicate, sometimes even more efficiently than the human users.
Increased replication speed
The replication speed of viruses depends on the replication strategy and the available
communication methods. Today's more powerful computer environments enable viruses and
worms to spread much faster than a decade ago. This table describes typical replication
speeds for the most common virus types.
The conclusion is that replication speed has increased dramatically over the past decade. This
emphasizes even further the fact that anti-virus software must be kept up to date to protect the
system efficiently. A typical update rate for anti-virus software has accordingly decreased
from monthly or bi-monthly to daily or real time.

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References
1. https://us.norton.com/internetsecurity-malware-what-is-a-computer-
virus
2. https://en.wikipedia.org/wiki/File:Virus_Blaster.jpg
3. https://en.wikipedia.org/wiki/Trojan_horse_(computing)
4. https://computer.howstuffworks.com/trojan-horse1.htm
5. https://en.wikipedia.org/wiki/Ransomware#WannaCry
6. https://searchsecurity.techtarget.com/definition/ransomware
7. https://en.wikipedia.org/wiki/Ransomware#/media/File:Metropolitan_
Police_ransomware_scam.jpg

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