Computer Viruses, Trojans and Worms

Computer Viruses

Computer Trojans

Computer Worms

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Computer Viruses

What is a Computer Virus?

To be defined as a virus, a program must:

"A computer virus is an exact cybernetic analogy to its biological reference"

Simple Definition

Virus Effects

Virus Components

Virus Types

Viruses are classified by the portion of the system they affect. There are six main types:

Boot Viruses

File Viruses

Multi-partite Viruses

Polymorphic Viruses

Meta Viruses

Virus Prevention

Information on Viruses

Dr. Solomon's War on Viruses

Computer Viruses and Security

Computer Trojans

Computer Trojans are simply malicious computer programs disguised as something useful. The major difference between viruses and Trojans is that viruses reproduce, while a Trojan is just a one time program which executes its payload as soon as the Trojan is executed. Trojans are the most common way of bringing a virus into a system. A current example of a Trojan is a program called pkz300b.exe which disguises itself as an archiving utility, but when run it will delete your entire hard drive.

Computer Worms

Computer Worms are reproducing programs that run independantly and travel across network connections. The main difference between viruses and worms is the method in which they reproduce and spread. A virus is dependant upon a host file or boot sector, and the transfer of files between machines to spread, while a worm can run completely independently and spread of its own will through network connections. An example of a worm is the famous internet worm of 1988: Overnight the worm copied itself across the internet, infecting every Sun-3 and VAX system with so many copies of itself that the systems were unusable. Eventually several sites disconnected themselves from the internet to avoid reinfection.

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This page was written by Andy Cochrane