Karachi Fun

What is a computer Virus?

A computer virus is just a computer program. But the behavior and purpose of making this type of programs is quite different for a normal program.

The word “Virus” has become a common term a lot of people use to refer to worms and Trojans too, which is not exactly correct.

• Virus -
  

A computer program that is capable of attaching to disks or other files and replicating itself repeatedly, typically without user knowledge or permission.

Some viruses attach to files so when the infected file executes, the virus also executes. Other viruses sit in a computer's memory and infect files as the computer opens, modifies or creates the files.

Some viruses display symptoms, and some viruses, damage files and computer systems, but neither symptoms nor damage are essential in the definition of a virus; a non-damaging virus is still a virus.

Virus is designed to spread from file to file on a single pc, it does not intentionally try to move to another pc, and it must replicate, and execute itself.

• Worm –

Unlike viruses worms are do not infect other computer program files. These are parasitic computer programs and replicate by creating copies on the same computer, or can send the copies to other computers via a network. Often spread via IRC (Internet Relay Chat)

A worm doesn’t need a host file to move from system to system, whereas a virus does. These are copy itself (intentionally move) from pc to pc, via networks, internet etc.
Worms spread more rapidly than viruses.

• Trojan Horse -

Trojan horse is a malicious program that pretends to be a benign application a Trojan horse program purposefully does something the user does not expect.

Trojans are not viruses since they do not replicate, but Trojan horse programs can be just as destructive.