This document discusses different types of computer viruses, including how they work and the damage they can cause. It explains that viruses replicate by infecting other programs, while worms and Trojan horses do not replicate but can still harm systems. The first virus was created in 1986. Viruses can infect computers through boot sectors, emails, files and networks. Common types are resident, multipartite, direct action, boot, encrypted and stealth viruses. Viruses may activate on certain dates or actions and can delete files, destroy data or display false messages.

1. Its Types…

2. A computer virus is a
type of malicious software
program , when executed,
replicates by reproducing itself or
infecting other computer
programs by modifying them.

3. Who created the first virus and
when ?
The first virus was created by the two
pakistani brothers Amjad Farooq
Alvi and Basit Farooq Alvi in 1986 and
was named as “Brain”

4. HOW DOES A VIRUS WORK?
Some viruses attack the
computer’s boot sector, the
area on the hard drive that
hosts the code for the start-up
routine. Such a root code virus
causes havoc because it runs
itself every time you switch on
the computer. Other viruses
are hidden in emails, games or
attached documents.

5. T H R E E T Y P E S O F C O M P U T E R I N F E C T I O N S
A R E :
1.VIRUSES
2.WORMS
3.TROJAN HORSES
Till now more than seventeen
million computer viruses are there
in the world !!!!

6. 1. RESIDENT VIRUSES: T H I S T Y P E O F V I R U S I S A
P E R M A N E N T W H I C H D W E L L S I N T H E R A M M E M O RY. F R O M
T H E R E I T C A N O V E R C O M E A N D I N T E R R U P T A L L O F T H E
O P E R AT I O N S E X E C U T E D B Y T H E S Y S T E M . E X : R A N D E X
2 . M U LT I PA RT I T E V I R U S E S : M U LT I PA RT I T E V I R U S E S A R E
D I S T R I B U T E D T H R O U G H I N F E C T E D M E D I A A N D U S U A L LY
H I D E I N T H E M E M O RY. G R A D U A L LY, T H E V I R U S M O V E S TO
T H E B O O T S E C TO R O F T H E H A R D D R I V E A N D I N F E C T S
E X E C U TA B L E F I L E S O N T H E H A R D D R I V E A N D L AT E R
A C R O S S T H E C O M P U T E R S Y S T E M . .
3 . D I R E C T A C T I O N V I R U S E S : T H E M A I N P U R P O S E O F T H I S
V I R U S I S TO R E P L I C AT E A N D TA K E A C T I O N W H E N I T I S
E X E C U T E D . W H E N A S P E C I F I C C O N D I T I O N I S M E T, T H E V I R U S
W I L L G O I N TO A C T I O N A N D I N F E C T F I L E S I N T H E D I R E C TO RY
O R F O L D E R T H AT I T I S I N A N D I N D I R E C TO R I E S T H AT A R E
S P E C I F I E D I N T H E A U TO E X E C . B AT F I L E PAT H .
Viruses

7. ZZZZ
4. Boot Virus : This type of virus affects the boot sector
of a floppy or hard disk. This is a crucial part of a disk, in
which information on the disk itself is stored together
with a program that makes it possible to boot the
computer from the disk.
5. Encrypted Viruses : This type of viruses consists
of encrypted malicious code, decrypted module. The
viruses use encrypted code technique which make
antivirus software hardly to detect them.
6. Stealth Viruses : Stealth Viruses is some sort of
viruses which try to trick anti-virus software by
intercepting its requests to the operating system. It has
ability to hide itself from some antivirus software
programs. Therefore, some antivirus program cannot

8. Trojans or Trojan
Horses :
Another unsavory breed
of malicious code (not a
virus as well) are Trojans
or Trojan horses, which
unlike viruses do not
reproduce by infecting
other files, nor do they
self-replicate like worms.
Worms : A worm is
technically not a virus,
but a program very
similar to a virus; it has
the ability to self-
replicate, and can lead to
negative effects on your
system and most
importantly they are
detected and eliminated
by antiviruses. EX : Code
Red

9. Activation of Virus
When the computer virus starts working, it is
called the activation of virus. A virus
normally runs all the time in the computer.
Different viruses are activated in different
ways. Many viruses are activated on a certain
data. For example, a popular virus“Friday,the
13th” is activated only if the date is 13 and the
day is Friday.

10. Causes of ComputerVirus :
 Infected Flash Drives or
Disks
 Email Attachments
 Infected websites
 Networks
 Pirated Software

11. Damages caused by virus
Computer virus cannot damage computer hardware. IT
may cause many damages to a computer system.
 A computer virus can damage data or software on the computer.
 It can delete some or all files on the computer system.
 It can destroy all the data by formatting hard drive.
 It may display a political or false message very few times.