The document provides an overview of computer viruses, explaining their nature as self-replicating programs that infect host systems, causing damage and data theft. It details symptoms of infection, types of malware, notable examples of viruses, and preventive measures, emphasizing the importance of antivirus software and safe computing practices. Additionally, it outlines how to identify and respond to a computer virus attack.

1. PREVENTING VIRUSES
AND OTHER MALICIOUS
CODE

2. WHAT IS COMPUTER
VIRUS?
Lesson 1

3. COMPUTER VIRUS
 is a type of computer program that, when executed, replicates itself
by modifying other computer programs and inserting its own code. If
this replication succeeds, the affected areas are then said to be
"infected" with a computer virus, a metaphor derived from biological
viruses.
 Computer viruses generally require a host program. The virus writes
its own code into the host program. When the program runs, the
written virus program is executed first, causing infection and damage.
 Computer viruses cause billions of dollars' worth of economic
damage each year.

4. COMPUTER VIRUS
 A computer virus is a self-spreading piece of software. The viruses
disrupt the normal functioning of a computer, damaging its software
or stealing its data.
 The first computer virus was created in 1971 to test whether
computer software could self-replicate.

5. BIOLOGICAL VIRUS
biological virus is a tiny
parasite relying on living cells
for survival. Viruses live at the
expense of the host, which can
be an animal, plant, or bacteria.
As soon as it has infected a host
cell, a virus starts reproducing,
invading other cells, and
spreading disease.

6. BIOLOGICAL VIRUS
computer virus shows
up on your Mac
uninvited and starts
reproducing itself. If
left unchecked, it can
cause a lot of damage.

7. WHAT ARE THE
SYMPTOMS OF A
COMPUTER VIRUSES?

8. 1.YOUR COMPUTER SLOWS DOWN
One of the most common computer virus symptoms is slow
down. You can know that your computer has been affected
by malware if your operating system, computer
applications, and internet speed begin to slow down. If you
note such a tendency and you’re not running heavy
applications or programs, there may be cause for alarm.

9. 2. CRASHING
If your system crash suddenly appears
or the infamous Blue Screen of Death
(BSOD) appears more often, then it’s
obvious that your computer isn’t
operating normally and you should
check it.

10. 3. POP-UPS
One of the most annoying
computer virus symptoms
are characterized by
unwanted pop-ups. If these
unexpected pop-ups
appear on your system,
know that your computer
has probably been affected
by spyware/virus/malware.

11. 4.HARD DRIVE MALFUNCTION
In case you have discovered
that your hard disk is
exhibiting unusually high
activity even when you aren’t
using it, consider checking for
malware. However, hard disk
malfunction can also be
caused by hardware failure.

12. 5.RUNNING OUT OF STORAGE SPACE
Computer virus symptoms can be triggered by
numerous malicious software through different methods
to fill your storage space and may eventually cause it to
crash.

13. 6.UNWANTED PROGRAMS OR MESSAGES
THAT START AUTOMATICALLY
Some of the warning signs that you should be suspicious about
include:
• Windows shutting down suddenly without reason
• Programs opening or closing automatically
• Strange windows as you boot
• Message from windows that you lost access to your drive

14. 7. DISABLED SECURITY SOLUTION
In case your antivirus doesn’t seem to work or if your update
module all of a sudden is disabled, make sure that you check
what has happened as soon as possible. There are some types
of malware that are built to disable computer security solutions
and leave your machine defenseless.access to your drive

15. 8.SENDING STRANGE MESSAGES
AUTOMATICALLY
The first step is to confirm whether the messages were sent
from your account. However, if you discover that you
weren’t the sender, then the messages were sent by an
uncontrollable application.

16. 9.UNUSUAL NETWORK ACTIVITY
Sometimes you may not be connected to the internet, and
you aren’t running any applications that can connect
themselves to the internet, but you still observe high
network activity. Such computer virus symptoms can be
confirmed by using a good antivirus.

17. 10. APPLICATIONS
If you have tried to start applications from the start menu or
desktop of your computer and nothing happens, then your
computer may be infected.

18. 11.ERROR MESSAGES
Your computer will know
when something is wrong
even before you do. One of
the noticeable computer
virus symptoms includes
messages that warn you of
missing files.

19. 12.ADVERTISEMENTS
Ads are common when
browsing. However, when
you see them when not
browsing, this could be a
sign of a virus.

20. 13.HARDWARE AND ACCESSORY PROBLEMS
In case you have problems with your
computer display, for instance color
problems or mixing pixels, this can be an
indication of malware in your computer.
Sometimes network printers also
malfunction if they become infected.

21. 14.SENT EMAILS
Viruses can be spread via emails. Therefore, if
you note that there are emails in your outbox
that you never sent or you receive suspicious
emails from a friend, they may be infected.

22. 15.COMPUTER MALFUNCTION
Computer viruses can cause your computer to
do all kind of strange things. When your
computer starts to open files on its own, or
acts like keys have been clicked, then you may
be experiencing computer virus symptoms.

23. TYPES OF VIRUSES
Lesson 2

24. 1. MALWARE
 Short for “malicious software,” malware comes in several forms and
can cause serious damage to a computer or corporate network.
There are various forms of malware ranging from viruses and worms
to Trojans and beyond. Malware is often seen as a catch-all term that
refers to any software designed to cause damage to a computer,
server, or network.
 Antivirus software is the most known product to protect your personal
devices against malware and is a great start to prevent potential
threats.While for enterprises, protecting your endpoint is essential to
quickly detect, prevent, and correct advanced threats to your
business.

25. 2. COMPUTER WORM
 The distinctive trait of a worm is that it can self-replicate and doesn’t
require human interaction to create copies and spread quickly and in
great volume. Most worms are spread though tricking internet users
and are designed to exploit known security holes in software.
 If a machine is infected, the worm can: corrupt files, steal sensitive
data, install a backdoor giving cybercriminals access to your
computer, or modify system settings to make your machine more
vulnerable.
 A computer worm is malware, just like a virus, but a worm takes a
copy of itself and propagates it to other users.

26. 3. SPAM
 Spam refers to unsolicited messages in your email inbox. From the
sender’s perspective, spam is a great way to get their message across
in an efficient and cost-effective way. While spam is usually
considered harmless, some can include links that will install
malicious software on your computer if the recipient clicks on it.

27. 4. PHISHING
 Created by cybercriminals attempting to
solicit private or sensitive information,
phishing schemes tend to be the starting
point of nearly all successful cyberattacks.
 Phishing schemes can disguise itself in many
forms, whether its posing as your bank or a
common web service, with the sole purpose
to lure you in by clicking links and asking
you to verify account details, personal
information, or passwords.

28. 5. BOTNET

29. Botnet malware is a network of computers that have been hijacked
or compromised, giving hackers the ability to control infected
computers or mobile devices remotely. When the malware is
launched on your computer or mobile device, it recruits your
infected device into a botnet, and the hacker is now able to control
your device and access all your data in the background without
your knowledge.
A botnet can consist of as few as ten computers or hundreds of
thousands, and when bots come together, they are a force to be
reckoned with. If a botnet hits your corporate website, it can make
millions of requests at once ultimately overloading the servers
knocking the website offline, slow web traffic, or affect
performance. As many businesses are aware, a website that is
offline or has a long lag time can be very costly, resulting in a loss
of customers or a damaged reputation.

30. WHAT CAUSES COMPUTER
VIRUSES?

31. Computer viruses are standard programs; only
instead of offering useful resources, these programs
can damage your device.
For a threat actor to execute a virus on your
machine, you must initiate execution. In some
cases, an attacker can execute malicious code
through your browser or remotely from another
network computer. Modern browsers have defenses
against local machine code execution, but third-
party software installed on the browser could have
vulnerabilities that allow viruses to run locally.

32. WHAT DOES A
COMPUTER VIRUS DO?

33. The way a computer virus acts depends on how it’s
coded. It could be something as simple as a prank
that doesn’t cause any damage, or it could be
sophisticated, leading to criminal activity and fraud.
Many viruses only affect a local device, but others
spread across a network environment to find other
vulnerable hosts.

34. EXAMPLES OF
COMPUTER VIRUS

35. 1. MORRIS WORM
Morris Worm or the “Great Worm”, which is
believed to be the pioneer among computer worms
distributed through the internet. Created to
highlight security flaws in Unix systems, its founder
Robert Morris, made a fatal error that transformed
the worm from a potentially harmless software to a
denial-of-service (DDoS) attack machine.

37. 2. NIMDA
A worm, a virus, and a Trojan horse all in one
sounds like something out of a horror movie. But it’s
actually a computer virus known as Nimda (admin
spelled backwards) that hit the internet back in
2001. Within an hour after its release, Nimda
reached the top spot of all reported attacks. No
wonder, since the worm used five different
transmission routes.

39. 3. ILOVEYOU
The virus used emails as a transmission channel,
disguising itself as a love letter from one of its victim’s
contacts. The malware was hidden in the attachment
called “LOVE-LETTER-FOR-YOU.TXT.vbs”. Clicking
on it activated a Visual Basic script (a programming
language which allows programmers to modify code),
and the worm started overwriting random files on the
user’s PC. The worm also sent copies of itself to all
contacts in the user’s address book.

41. 4. SQL SLAMMER
 Outages in 911 service in Seattle,the crash of the Bank of America’s
ATM service, and cancellation of several Continental Airlines flights -
these are just a few examples of what SQL Slammer (or simply
Slammer) is capable of.
 It sparked at 05:30 UTC on January 25, 2003, infecting its first server.
Once the job was done, Slammer spread rapidly, doubling the number
of victims every few seconds, and just ten minutes after it was released
in the wild, the number of infected computers grew to 75,000.
 Slammer dramatically slowed down worldwide internet traffic, brought
down several important systems, caused a huge panic and more than
one billion dollars of damage.

43. 5. STUXNET
The destructive power of computer viruses can
make them weapons of mass digital destruction,
and Stuxnet became the first one. Unlike any other
virus or malware of that time, Stuxnet was
developed by the US and Israeli government
engineers to disrupt Iran’s nuclear program. Spread
via a USB thumb drive, it targeted Siemens
industrial control systems, causing centrifuges to
mysteriously fail and self-destroy at a record rate.

45. 6. CRYPTOLOCKER
CryptoLocker is not like a typical computer virus that
causes harm and spreads itself. It’s ransomware: a kind
of malware that takes your files hostage, holding them
for ransom. CryptoLocker used a trojan disguised as a
PDF file that was spread through email attachments.
Surprisingly enough, CryptoLocker caused no harm to
the computer itself and didn’t show up until the
encryption was done. If you haven’t backed up your files,
the only way to restore them was by paying a ransom.

47. 7. CONFICKER
If there is a flaw in the system, somewhere down the
line, it will undoubtedly be exploited. Conficker,
Downup, Downadup, Kido - these are all computer
virus names that appeared on the internet in 2008. It
used the MS08-067 Windows system vulnerability
and advanced malware techniques to propagate and
install itself into the system. These techniques
included copying itself to shared folders and
exploiting the AutoRun utility for removable media.

49. 8. TINBA
Tinba is the pet name for the Tiny Banker Trojan that
hit the headlines in 2016. As the name suggests, its
main target was financial institution websites. Tinba
used man-in-the-browser attacks and network
sniffing to get users’ banking information.

51. 9. SHLAYER
Shlayer disguised itself as updates for Adobe Flash
Player (that’s where its name comes from). When
launched, it ran a series of shell scripts to proliferate
various adware or potentially unwanted applications.
In most cases, users got the Shlayer virus when
visiting untrustworthy Torrent websites, clicking on
the advertisements, or downloading shady files.

52. HOW TO PREVENT
COMPUTER VIRUSES?

53. 1. INSTALL ANTIVIRUS SOFTWARE
Antivirus should run on any
device connected to the
network. It’s your first defense
against viruses. Antivirus
software stops malware
executables from running on
your local device.

54. 2.DON’T OPEN EXECUTABLE EMAIL
ATTACHMENTS
Many malware attacks
including ransomware start
with a malicious email
attachment. Executable
attachments should never be
opened, and users should
avoid running macros
programmed into files such as
Microsoft Word or Excel.

55. 3. KEEP YOUR OPERATING SYSTEM
UPDATED
Developers for all major
operating systems release
patches to remediate common
bugs and security
vulnerabilities. Always keep
your operating system
updated and stop using end-
of-life versions (e.g., Windows
7 or Windows XP).

56. 4. AVOID QUESTIONABLE WEBSITES
Older browsers are vulnerable
to exploits used when just
browsing a website. You
should always keep your
browser updated with the
latest patches, but avoiding
these sites will stop drive-by
downloads or redirecting you
to sites that host malware.

57. 5.DON’T USE PIRATED SOFTWARE
Free pirated software might be
tempting, but it’s often
packaged with malware.
Download vendor software
only from the official source
and avoid using software
that’s pirated and shared.

58. 5.DON’T USE PIRATED SOFTWARE
Free pirated software might be
tempting, but it’s often
packaged with malware.
Download vendor software
only from the official source
and avoid using software
that’s pirated and shared.

59. ANTI-VIRUS SOFTWARE

60. Anti-Virus Software that is created specifically to help
detect, prevent and remove malware (malicious software).
Antivirus is a kind of software used to prevent, scan, detect
and delete viruses from a computer. Once installed, most
antivirus software runs automatically in the background to
provide real-time protection against virus attacks.

61. 1. AVAST! FREE ANTIVIRUS
Avast Antivirus is a family of cross-platform internet
security applications developed by Avast for
Microsoft Windows, macOS, Android and iOS. ... It is
a cross-platform solution that includes antivirus
protection, web threat scanning, browser
protection, and a cloud management console.

62. 2. PANDA CLOUD ANTIVIRUS
Panda Dome is 100% safe to use.
It is a legitimate antivirus that
comes from a highly reputable
cybersecurity company. It uses
advanced scanning technology to
block the latest malware and
cyberattacks. It's designed to
protect against the latest malware
threats, including viruses,
spyware, and ransomware.

63. 3. MICROSOFT SECURITY ESSENTIALS
Microsoft Security Essentials is an
antivirus software product that
provides protection against
different types of malicious
software, such as computer
viruses, spyware, rootkits, and
trojan horses.

64. 4. AVIRA ANTIVIR PERSONAL EDITION
All versions of Avira Antivirus
offer Real-time protection against
malware. This feature monitors
and scans all the files you access,
copy, or otherwise interact with,
letting you know if they are safe
or infected. In case of danger,
Avira Antivirus won't let the
suspicious file make changes to
your device

65. 5. AVG ANTI-VIRUS FREE EDITION
AVG AntiVirus for Android guards
your mobile phone against
malware attacks and threats to
your privacy. We give you on-the-
go protection against unsafe
apps, anti-theft locker & tracker,
and plenty more security and
performance features.

66. 6. COMODO ANTIVIRUS
Comodo Antivirus is a fairly good
antivirus program. Prevents
viruses and malware from causing
harm to your computer before it's
too late. Cloud-based antivirus
scanning helps users scan and
identify malicious files even if
they are not equipped with up-to-
date virus definitions.

67. 7. IMMUNET PROTECT FREE
a malware and antivirus
protection system that utilizes
cloud computing to provide
enhanced community-based
security. It works in the cloud,
keeping your computer working
free. It offers good protection
against bots, worms, viruses,
trojans, keyloggers, and spyware,
so a full protection

68. 8. PC TOOLS ANTIVIRUS FREE
 PC Tools AntiVirus is one of the most
basic antivirus programs you will find.
PC Tools iAntiVirus is free antivirus
software for Intel based Apple
Macintosh computers running Mac OS
10.5 (Leopard) and Mac OS 10.6
(Snow Leopard) initially released in
June 2008, used to detect and remove
malware, spyware and malicious
exploits, using both signature-based
and heuristic detection.

69. 9. MALWAREBYTES
Malwarebytes offers one of the
best antivirus programs to protect
computers against malware,
hacks, viruses, ransomware, and
other ever-evolving threats to
help support a safe online
antivirus experience. ... It
removes all traces of malware,
blocks the latest threats, and is a
fast virus scanner.

70. 10. CLAMWIN FREE ANTIVIRUS
An open-source program
ClamWin, is reasonably good
protection for your computer. The
users receive several useful
features free of charge.
Specifically, using ClamWin
antivirus, you have an opportunity
to scan your device, protect it
against viruses and malware.