Types of Computer Viruses
What is a Computer Virus ?
A potentially damaging computer programme capable of reproducing
itself causing great harm to files or other programs without permission
or knowledge of the user.
Types of viruses :-
The different types of viruses are as follows-
1) Boot Sector Virus :-
Boot sector viruses infect either the master
boot record of the hard disk or the floppy drive. The boot record
program responsible for the booting of operating system is replaced by the virus. The
virus either copies the master boot program to another part of the hard disk or
overwrites it. They infect a computer when it boots up or when it accesses the infected
floppy disk in the floppy drive. i.e. Once a system is infected with a boot-sector virus,
any non-write-protected disk accessed by this system will become infected.
Examples of boot- sector viruses are Michelangelo and Stoned.
2) File or Program Viruses :-
Some files/programs, when executed, load the virus in
the memory and perform predefined functions to infect the system. They infect
program files with extensions like .EXE, .COM, .BIN, .DRV and .SYS .
Some common file viruses are Sunday, Cascade.
3) Multipartite Viruses :-
A multipartite virus is a computer virus that infects multiple
different target platforms, and remains recursively infective in each target. It attempts to
attack both the boot sector and the executable, or programs, files at the same time. When the virus attaches to the boot sector, it will in turn affect the system’s files, and
when the virus attaches to the files, it will in turn infect the boot sector.
This type of virus can re-infect a system over and over again if all parts of the virus are
Ghostball was the first multipartite virus, discovered by Fridrik Skulason in October
Other examples are Invader, Flip, etc.
4) Stealth Viruses :-
These viruses are stealthy in nature means it uses various
methods for hiding themselves to avoid detection. They sometimes remove themselves
from the memory temporarily to avoid detection by antivirus. They are somewhat
difficult to detect. When an antivirus program tries to detect the virus, the stealth virus
feeds the antivirus program a clean image of the file or boot sector.
5) Polymorphic Viruses :-
Polymorphic viruses have the ability to mutate implying that
they change the viral code known as the signature each time they spread or infect.
Thus an antivirus program which is scanning for specific virus codes unable to detect
6) Macro Viruses :-
A macro virus is a computer virus that “infects” a Microsoft Word
or similar application and causes a sequence of actions to be performed automatically
when the application is started or something else triggers it. Macro viruses tend to be
surprising but relatively harmless.A macro virus is often spread as an e-mail virus. Well-known examples are Concept Virus and Melissa Worm.