This document discusses computer viruses and operating systems. It begins by defining an operating system as an interface between the user and computer hardware that manages tasks like file handling and device control. A GUI is described as a graphics-based user interface using elements like windows and icons. Computer viruses can spread via flash drives, email attachments, and internet downloads. Some notable viruses mentioned include ILOVEYOU from 2000, Blaster worm of 2003, and MyDoom of 2004. Types of viruses include boot sector, direct action, and resident viruses. The document concludes by recommending antivirus software and caution when downloading files to prevent virus infections.

1. 1. What is an Operating System?
2. What is meant by GUI?
3. How do computer viruses infection occur. (Give at
least 2)
4. What year the ILOVEYOU VIRUS was developed?
5. What virus infected more than 10 million machines
worldwide that lacked the appropriate patch (software
bug controller).
6. Give atleast 3 types of computer viruses?
7. How to prevent computer viruses?

2. 1. An Operating System (OS) is an interface between the computer user
and computer hardware. An operating system is a software that
performs all the basic tasks like file management, memory
management, process management, handling input and output, and
controlling peripheral devices such as disk drives and printers.
2. A user interface that displays graphics in addition to text when it
communicates with the user. It utilizes windows, icons, menus, and
pointers.
3. It can arrive on a flash drives. They most easily spread by attachments
in e-mail messages. Computer viruses also spread by using
downloads on the Internet.
4. 2000 created by Onel de Guzman from Ph
5. Blaster worm, 2003
6. Boot sector virus, direct action virus, resident virus
7. Exercise caution when downloading files from the Internet.
– Ensure that the source is a legitimate and reputable one.

4. • It is an interface between computer
user and computer hardware.
• It is software which performs all the
basic tasks like file management,
memory management, process
management, handling input and
output, and controlling peripheral
devices such as disk drives,
printers and etc.

5. • It is the most important program that runs on a
computer.
• It is considered as the “brain” of the computer system.
• It is used to run other programs such as MS Office
and all other programs installed in the computer
system.
• Without the OS the computer system is practically
useless.
• Is a collection of programs that controls how the CPU,
memory, and I/O devices work together.

6. • The OS is the manager of all the computer system’s
hardware and software.
• In layman’s term, the OS is a computer program that
provides an interface for the user to communicate with
the computer.

7. 1. Memory Management - refers to the management of
Primary Memory or Main Memory. Main memory is a
large array of words or bytes where each word or
byte has its own address.
An Operating System does the following activities for
memory management.
• Keeps track of primary memory, i.e., what parts of it are in
use by whom, and what parts are not in use.
• In multiprogramming, the OS decides which process will get
memory when and how much.
• Allocates the memory when a process requests it to do so.
• De-allocates the memory when a process no longer needs it
or has been terminated.

8. 2. Processor Management – in a multiprogramming
environment, the OS decides which process gets
the processor when and for how much time. This
function is called process scheduling.
An Operating System does the following activities for
processor management.
• Keeps track of processor and status of the process. The
program responsible for this task is known as a traffic
controller.
• Allocates the processor (CPU) to a process.
• De-allocates processor when a process is no longer
required.

9. 3. Device Management – an Operating System
manages device communication via their
respective drivers. It does the following activities
for device management
• Keeps track of all devices. The program responsible for
this task is known as the I/O controller.
• Decides which process gets the device when and for how
much time.
• Allocates the device in an efficient way.
• De-allocates devices.

10. 4. File Management – A file system is normally
organized into directories for easy navigation
and usage. These directories may contain files
and other directions.
An Operating System does the following activities for file
management.
• Keeps track of information, location, uses, status etc. The
collective facilities are often known as file system.
• Decides who gets the resources.
• Allocates the resources.
• De-allocates the resources.

11. 5. Security – By means of passwords and similar other
techniques, it prevents unauthorized access to
programs and data.
6. Control Over System Performance – Recording
delays between a request for a service and
response from the system.
7. Job Accounting – Keeping track of time and
resources used by various jobs and users.

12. 8. Error Detecting Aids – Production of dumps, traces,
error messages, and other debugging and error-
detecting aids.
9. Coordination Between Other Software And Users –
Coordination and assignment of compilers,
interpreters, assemblers, and other software to the
various users of the computer systems.

13. • Maximize the productivity of a computer system
by operating in the most efficient manner and
minimizing the amount of human intervention.
• Most modern OSes utilizes a user interface to
make interacting with the computer easy.
• The goal of user interface is to be “user-friendly”,
which means that the software can be used easily
by individuals with limited training.

14. • A user interface that displays graphics in addition
to text when it communicates with the user.
• It utilizes windows, icons, menus, and pointers.

15. Is a malicious program that self-replicates by copying
itself to another program. In other words, the computer virus
spreads by itself into other executable code or documents.
The purpose of creating a computer virus is to infect
vulnerable systems, gain admin control and steal user
sensitive data. Hackers design computer viruses with
malicious intent and prey on online users by tricking them.
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.

16. • It can arrive on a flash drives
• They most easily spread by
attachments in e-mail messages.
• Computer viruses also spread by using
downloads on the Internet.

17. 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.

18. • 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.

19. • 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.
• Disks or disk drives are inaccessible. Your flash
drive won’t open and there’s an error message
occur “Disk drive is inaccessible”.

20. • The computer runs slower than usual.
• The computer stops responding, or it locks up
frequently.
• The computer restarts on its own every few
minutes and does not run as usual.
• Computer applications do not work correctly.
• Disks or disk drives are inaccessible.
• There’s a double extension on attachment that’s
recently opened (e.g. .jpg, .gif, or .exe).

21. • Antivirus program cannot be installed or
won’t run on the computer.
• Antivirus program cannot be restarted or is
disabled for no reason.
• New icons appear on the desktop that are
not placed there or not even associated with
any recently installed programs.

22. How can you help protect your devices against
computer viruses? Here are some of the things you can
do to help keep your computer safe.
• Use a trusted antivirus product, such as Norton
AntiVirus Basic, or Windows Defender, and keep it
updated with the latest virus definitions.
• Avoid clicking on any pop-up advertisements.
• Always scan your email attachments before opening
them.
• Always scan the files that you download using file-
sharing programs.

23. Best practices for detecting and preventing viruses.
1. Do not open any files attached to an email from an
unknown, or untrustworthy source or even if it appears to
come from someone you know if the subject line is
questionable.
– If the need to do so is there, always save the file to your
hard drive before doing so.
2. Delete chain emails and junk email.
– Do not forward or reply to any to them. These types of
email are considered spam, which is unsolicited, intrusive
mail that clogs up the network.

24. Best practices for detecting and preventing viruses.
3. Exercise caution when downloading files from the
Internet.
– Ensure that the source is a legitimate and reputable one.
4. When in doubt, always err on the side of caution.
– Do not open, download, or execute any files or email
attachments.
– Not executing is the most important of these.

25. • Boot Sector Virus – This type of virus infects the
master boot record and it is challenging and a
complex task to remove this virus and often requires
the system to be formatted. Mostly it spreads through
removable media.
• Direct Action Virus – This is also called non-
resident virus, it gets installed or stays hidden in the
computer memory. It stays attached to the specific
type of files that it infect. It does not affect the user
experience and system’s performance.

26. • Resident Virus – Unlike direct action viruses, resident
viruses get installed on the computer. It is difficult to
identify the virus and it is even difficult to remove a
resident virus. The resident viruses are troublesome due
to the reason they can run unnoticed by antivirus and
antimalware software by hiding in the system’s RAM.
• Multipartite Virus – This type of virus spreads through
multiple ways. It infects both the boot sector and
executable files at the same time.
• Spacefiller Virus – This is also called “Cavity Viruses”.
This is called so as they fill up the empty spaces between
the codes and hence does not cause any damage to the
file.

27. • Polymorphic Virus – These types of viruses are
difficult to identify with a traditional anti-virus
program. This is because the polymorphic virus
alters its signature pattern whenever it replicates.
Since virus removal programs depend on identifying
signatures of malware, these viruses are carefully
designed to escape detection and identification.
When security software detects a polymorphic virus,
the virus modifies itself thereby; it is no longer
detectable using the previous signature.

28. • Overwrite Virus – This type of virus deletes all the
files that it infects. The only possible mechanism to
remove is to delete the infected files and the end-user
has to lose all the contents in it. Identifying the
overwrite virus is difficult as it spreads through emails.

29. • File Infectors – Few file infector viruses come
attached with program files, such as .com or .exe
files. Some file infector viruses infect any program for
which execution is requested, including .sys, .ovl,
.prg, and .mnu files. Consequently, when the
particular program is loaded, the virus is also loaded.
Besides these, the other file infector viruses come as
a completely included program or script sent in email
attachments.

30. • Macro Viruses – As the name suggests, macro viruses
particularly target macro language commands in
applications like Microsoft Word. The same is implied on
other programs too.
In MS Word, the macros are keystrokes that are
embedded in the documents or saved sequences for
commands. The macro viruses are designed to add their
malicious code to the genuine macro sequences in a Word
file. However, as the years went by, Microsoft Word
witnessed disabling of macros by default in more recent
versions. Thus, cybercriminals started to use social
engineering schemes to target users. In the process, they
trick the user and enable macros to launch the virus.

31. • Rootkit Viruses – a malware type which secretly
installs an illegal rootkit on an infected system. This
opens the door for attackers and gives them full control
of the system. The attacker will be able to fundamentally
modify or disable functions and programs. Like other
sophisticated viruses, the rootkit virus is also created to
bypass antivirus software. The latest versions of major
antivirus and antimalware programs include rootkit
scanning.

32. • System or Boot-record Infectors – The Boot-record
Infectors infect executable code found in specific
system areas on a disk. As the name implies, they
attach to the USB thumb drives and DOS boot sector
on diskettes or the Master Boot Record on hard disks.
Boot viruses are no more common these days as the
latest devices rely less on physical storage media.

33. • Late 1940s, John von Neumann proposed that it
was theoretically possible for a computer program to
replicate.
• 1950s, the theory was tested at Bell Laboratories
through the development of Core Wars, where
players created tiny computer programs that
attacked, erased, and tried to propagate on an
opponent's system.

34. • 1971, the Creeper program, often regarded as the first
virus, was created by Bob Thomas of BBN. Creeper
was actually designed as a security test to see if a self-
replicating program was possible. It was—sort of. With
each new hard drive infected, Creeper would try to
remove itself from the previous host. Creeper had no
malicious intent and only displayed a simple message:
"I'M THE CREEPER. CATCH ME IF YOU CAN!"

35. • 1982, 15-year-old Rich Skrenta developed Elk
Cloner, the first computer virus—not named that yet—
that spread outside a laboratory. Skrenta created it as
a joke for his friends, whose Apple II computers
became infected by inserting a diskette with a game
that hid the virus.
• 1983, American Electrical Engineer Fred
Cohen, coined the term virus to describe a self-
replicating computer program.
• 1985, the first Trojan horses appeared, posing as a
graphics-enhancing program called EGABTR and as
a game called NUKE-LA.

36. • 1986, the Brain virus appeared and spread
worldwide by 1987. Created by the two Pakistani
brothers, Basit and Amjad Farooq Alvi.
• 1988, two new viruses appeared: the Stone virus,
and Internet worm.
• 1989, the Dark Avenger, the first fast infector virus.
Was a pseudonym of a computer virus writer from
Sofia, Bulgaria.
• 1990, first Polymorphic virus called 1260 or V2PX.
Created by Mark Washburn.
• 1995, the WinWord Concept virus.

37. • 1999, the Melissa macro virus, which costs
corporations millions of dollars due to computer
downtime and lost productivity. Created by David L.
Smith.
• 2000, the VBS_LOVELETTER virus, a.k.a. the Love
Bug and the ILOVEYOU virus in which losses were
estimated at $10 billion, with a 1:5 ratio of infection.
Created by Onel de Guzman from Philippines.
• 2003, the Blaster worm infected more than 10 million
machines worldwide that lacked the appropriate patch
(software bug corrector).

38. • 2003, the SoBig worm, considered as the fastest
spreading virus, capable of sending massive amounts
of junk e-mail or spam.
• January 2004, the MyDoom virus set a new record,
spreading even faster than SoBig, causing even
more damage.

39. • 2014, One of the most recent of the major viruses came out,
Heartbleed burst onto the scene and put servers across the
Internet at risk. Heartbleed, unlike viruses or worms, stems
from vulnerability in OpenSSL, a general purpose, open source
cryptographic library used by companies worldwide. OpenSSL
periodically sends out "heartbeats" to ensure that secure
endpoints are still connected. Users can send OpenSSL a
specific amount of data and then ask for the same amount
back—for example, one byte. If users claim they're sending the
maximum allowed, 64 kilobytes, but only send a single byte, the
server will respond with the last 64 kilobytes of data stored in
RAM, notes security technologist, Bruce Schneier, which could
include anything from user names to passwords to secure
encryption keys.

40. Thank You!