This document provides information about computer viruses, including what they are, how they spread, different types of viruses, signs that a computer may be infected, and ways to protect against viruses using anti-virus software. It defines viruses and explains that they can replicate and spread without permission. The document then describes several types of viruses like memory resident viruses, direct action viruses, overwrite viruses, and others. It also lists common signs of infection and explains how anti-virus software works to detect and remove viruses, protecting users and their devices.

2. What is a Virus?
Computer virus is a software program
written with malicious intentions.
Computer virus is a harmful software
program written intentionally to enter a
computer without the user's permission or
knowledge. It has the ability to replicate
itself, thus continuing to spread. Some
viruses do little but replicate, while others
can cause severe harm or adversely affect
the program and performance of the
system. A virus should never be assumed
harmless and left on a system.

3. How Do I Know I’ve Got Virus in My
Computer?
You may not notice that your computer is
under attack until you realize something is
missing or wrong when you open an
attachment or a program with virus.
Here is couple of signs which may show
you that your computer is under attack.

4. • Your computer work slower than it was.
• Your computer freezes frequently or doesn’t open
properly
• Your computer restarts in every couple minutes.
• Your system doesn’t work properly and restarts
itself
• Applications in your computer doesn’t work
properly.
• You cannot reach to discs and drivers
• You cannot print
• You are seeing unusual errors
• You see messed up-shaped menus

5. Types of Computer Viruses
 There are number of computer viruses that can impede
the functioning of your computer system.

6. Computer viruses usually spread in one of
three ways: from removable media; from
downloads off the Internet; and from e-mail
attachments.
Although the Internet gets a bad rap as a
source of viruses, you're no more likely to
contract a virus from the Web than you are
from packaged software. Still, scan everything
you download, and update your antivirus
software regularly.
The Spread of Computer Viruses

7. Why Do People Create Computer
Viruses?
-To take control of a computer and use it for
specific tasks
-To generate money
-To steal sensitive information (credit card
numbers, passwords, personal details, data etc.)
-To prove a point, to prove it can be done, to
prove ones skill or for revenge purposes
-To cripple a computer or network

8. Memory Resident Virus
 These viruses fix themselves in the computer memory and
get activated whenever the OS runs and infects all the files
that are then opened.
 This type of virus hides in the RAM and stays there even
after the malicious code is executed. It gets control over
the system memory and allocate memory blocks through
which it runs its own code, and executes the code when
any function is executed.
 Examples: Randex, CMJ, Meve, and MrKlunky

9. Direct Action Viruses
 The main purpose of this virus is to replicate(copy) and
take action when it is executed. When a specific condition
is met, the virus will go into action and infect files in the
directory or folder that are specified in the AUTOEXEC.BAT
file path. This batch file is always located in the root
directory of the hard disk and carries out certain
operations when the computer is booted.
 The viruses keep changing their location into new
files whenever the code is executed, but are
generally found in the hard disk's root directory.
 Target: It can corrupt files. Basically, it is a
file-infecter virus.
 Examples: Vienna virus

10. Overwrite Viruses
 A virus of this kind is characterized by the fact that it
deletes the information contained in the files that it infects,
totally useless once they have been infected.
 The virus replaces the file content. However, it does not
change the file size.
 Examples: Way, Trj.Reboot, Trivial.88.D

11. Boot Sector Virus
 This type of virus affects the boot sector of a hard disk. This
is a crucial part of the disk, in which information of the disk
itself is stored along with a program that makes it possible
to boot (start) the computer from the disk. This type of
virus is also called Master Boot Sector Virus or Master Boot
Record Virus.
 It hides in the memory until DOS accesses the floppy disk,
and whichever boot data is accessed, the
virus infects it.
 Examples: Polyboot.B, AntiEXE

12. Macro Virus
 Macro viruses infect files that are created using certain
applications or programs that contain macros, like .doc, .xls,
.pps, .mdb, etc. These mini-programs make it possible to
automate series of operations so that they are performed
as a single action, thereby saving the user from having to
carry them out one by one. These viruses automatically
infect the file that contains macros, and also infects the
templates and documents that the filecontains. It is
referred to as a type of e-mail virus.
 These hide in documents that are
shared via e-mail or networks.
 Examples: Relax, Melissa.A, Bablas,
O97M/Y2K

13. Directory Virus
 Directory viruses (also called Cluster Virus/File System
Virus) infect the directory of your computer by changing the
path that indicates the location of a file. When you execute
a program file with an extension .EXE or .COM that has
been infected by a virus, you are unknowingly running the
virus program, while the original file and program is
previously moved by the virus. Once infected, it becomes
impossible to locate the original files.
 It is usually located in only one location of the
disk, but infects the entire program in the
directory.
 Examples: Dir-2 virus

14. Polymorphic Virus
 Polymorphic viruses encrypt or encode themselves in a
different way (using different algorithms and encryption
keys) every time they infect a system. This makes it
impossible for antivirus software to find them using string
or signature searches (because they are different in each
encryption). The virus then goes on to create a large
number of copies.
 Examples: Elkern, Marburg, Satan Bug
and Tuareg

15. Companion Viruses
 Companion viruses can be considered as a type of file
infector virus, like resident or direct action types. They are
known as companion viruses because once they get into the
system they 'accompany' the other files that already exist. In
other words, to carry out their infection routines,
companion viruses can wait in memory until a program is
run (resident virus), or act immediately by making copies of
themselves (direct action virus).
 These generally use the same filename and create a
different extension of it. For example: If there is a file
"Me.exe", the virus creates another file named "Me.com"
and hides in the new file. When the system calls the
filename "Me", the ".com" file gets executed (as ".com" has
higher priority than ".exe"), thus infecting the system.
 Examples: Stator, Asimov.1539 and Terrax.1069

16. FAT Virus
 The file allocation table (FAT) is the part of a disk used to
store all the information about the location of files,
available space, unusable space, etc.
 FAT virus attacks the FAT section and may damage crucial
information. It can be especially dangerous as it prevents
access to certain sections of the disk where important files
are stored. Dama
 ge caused can result in loss of information from individual
files or even entire directories.
 Examples: Link Virus

17. Web Scripting Virus
 Many web pages include complex codes in order to create
an interesting and interactive content. This code is often
exploited to bring about certain undesirable actions.
 The main sources of web scripting viruses are the web
browsers or infected web pages.
 Examples: JS.Fortnight is a virus that spreads through
malicious e-mails.

18. Worms
 A worm is a program very similar to a virus; it has the
ability to self-replicate and can lead to negative effects on
your system. But they can be detected and eliminated by
an antivirus software.
 These generally spread through e-mails and networks. They
do not infect files or damage them, but they replicate so
fast that the entire network may collapse.
 Examples: PSWBugbear.B, Lovgate.F, Trile.C,
Sobig.D, Mapson

19. Trojans
 Another unsavory breed of malicious code are Trojans or
Trojan horses, which unlike viruses, do not reproduce by
infecting other files, nor do they self-replicate like worms.
In fact, it is a program which disguises itself as a useful
program or application.
 These viruses copy files in your computer (when their
carrier program is executed) that can damage your data,
and even delete it. The attacker can also program the
trojans in such a manner that the
information in your computer is accessible
to them.
 Examples: Trojan.Vundo

20. Disadvantages od Viruses
 Format hard disk
 Copy, rename and delete files
 Modify files dates and extensions
 Display false message every few times
 Damage data
 Damage software

21. Disadvantages od Viruses
 Computer runs slowly
 Random restarts
 Unknown and uninstalled icons on desktop
 Icons change in appearance
 System memory and disk space is reduced
 New windows open up at an alarming rate
 Error messages on regular basis
 Files mysteriously disappear

22. Computer Anti-Virus
 Antivirus software is a computer program that detects,
prevents, and takes action to disarm or remove malicious
software programs, such as viruses and worms.
 There are certain types of anti-viruses.

23. Best Computer Anti-Viruses
 There are so many anti-viruses which works against viruses
but some anti-viruses are trusted and are very famous.
 There are 10 ranked anti-viruses by toptenreviews.com
http://anti-virus-software-review.toptenreviews.com/

24. List of all Anti-Viruses
• Avira Antivirus
• Avast Antivirus
• AVG Antivirus
• Immunet Protect
• Emsisoft Antimalware
• Digital Patrol
• K7 Antivirus
• eScan Antivirus
• Comodo Antivirus
• Dr.Web Antivirus
• Digital Defender Antivirus
• Norman Antivirus
• Clam Antivirus
• F-Prot Antivirus
• Kaspersky Antivirus
• Vipre Antivirus
• Trend Micro Antivirus
• Sophos Antivirus
• Panda Cloud Antivirus
• Tizer Secure
• FortiClient Antivirus
• Solo Antivirus
• Twister Antivirus
• Ad-Aware Internet Security
• VBA32 Antivirus
• Quick Heal Antivirus
• Rising Antivirus
• Kingsoft Antivirus
• Vexira Antivirus
• Arcavir Antivirus
• nProtect Antivirus

25. List of all Anti-Viruses
• ViRobot Antivirus
• Antiy Antivirus
• System Shield Antivirus
• CSAM Antivirus
• Blue Point Security
• Microsoft Security Essentials
• Net Protector Antivirus
• eAcceleration Antivirus
• Zillya! Antivirus
• Paretologic Antivirus Plus
• Blink Personal
• Drive Sentry
• FSB Antivirus
• Norton Antivirus
• Coranti Antivirus
• Ashampoo Anti-malware
• McAfee Antivirus
• Trustport Antivirus
• Webroot Antivirus
• My Free Antivirus
• F-Secure Antivirus
• Bullguard Antivirus
• CA Antivirus
• Cyber Defender
• Protector Plus
• G Data Antivirus
• Max Secure Antivirus
• ClamWin
• Spyware Doctor
• Outpost Antivirus
• Zone Alarm Antivirus
• BitDefender Antivirus

26. Advantages of Anti-Virus
 Protecting Personal Data
If you have an anti virus then you
don’t need to worry
about the virus that it will:
 Format hard disk
 Copy, rename and delete files
 Modify files dates and extensions
 Display false message every few
times
 Damage data
 Damage software

27. Advantages of Anti-Virus
 Computer runs slowly
 Random restarts
 Unknown and uninstalled icons on
desktop
 Icons change in appearance
 System memory and disk space is
reduced
 New windows open up at an
alarming rate
 Error messages on regular basis
 Files mysteriously disappear

28. Advantages of Anti-Virus
 Protecting Personal Information
• Hackers and viruses go hand in hand. A good anti-virus
program will protect you while you surf the Internet,
preventing hackers from gaining access to personal things
such as credit card information and bank account access.
The firewall feature included with most anti-virus software
will block any unauthorized incoming connections
to your network or computer,
preventing hackers from
digging their hooks into your
life and your computer.