What is a virus and how is it different from worms and trojans?

A virus can be described as a small programme that is specifically written to subvert the normal operations of a computer, thereby making it malfunction.

india Updated: Dec 10, 2003 19:07 IST

What is a virus?

A virus is a programme written specifically to subvert the normal operations of a computer, thereby making it malfunction. The sole aim of a virus is to cause destruction.

A virus piggybacks on real programmes. For example, a virus might attach itself to a programme such as a Word document. Each time the infected file runs, the virus runs too and it has the chance to reproduce (by attaching to other programmes).

Such malicious programmes are known as viruses as they share some of the traits of biological viruses. A computer virus passes from computer to computer like a biological virus passes from person to person.

Largely, there are five kinds of viruses:

Boot sector viruses infect the boot sector (an area that forms the first track of the disk and contains information that is required to boot the computer) of your hard disk or floppy disk.

File viruses infect executable files (such as .com, .exe, .ole, etc).

Stealth viruses attempt to hide not only from the operating system but also from the anti-virus software, which makes them extremely difficult to identify.

Polymorphic viruses not only hide from the anti-virus software but also keep changing their appearance. In order to detect them, the anti-virus scanner should be able to conduct algorithmic scanning, besides just string-based scanning.

Multi-partite viruses are the worst of the lot as they can infect the boot sector as well as executable files. They also possess characteristics of Polymorphic viruses, which makes them extremely lethal.

First Published: Dec 06, 2003 00:00 IST