-: Computer Virus :-
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 not eradicated.
Ghostball was the first multipartite virus, discovered by Fridrik Skulason in
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 it's presense.
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.
7) Trojan horses :-
A Trojan horse is simply a computer program that claims to
do one thing (it may claim to be a game) but instead does damage when you run
it (it may erase your hard disk). When loaded onto your machine, a Trojan horse
can capture information from your system -- such as user names and passwords or
could allow a malicious hacker to remotely control your computer.
Trojan horses have no way to
8) Worms :-
A worm is a computer program that has the ability to copy
itself from machine to machine. Worms normally move around and infect other
machines through computer networks. Worms eat up storage space and slow down
the computer. But worms don't alter or delete files.