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The Difference Between a Trojan Horse, Virus, and a Worm Close Window
This page describes the difference between three very common outbreaks that can affect your computer. It is important to stay informed about virus related information.

A Trojan Horse program 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.

Many people use the term to refer only to non-replicating malicious programs, thus making a distinction between Trojans and viruses.

A Virus is a program or piece of code that causes an unexpected, usually negative, event. Viruses are often disguised as games or images with clever marketing titles such as "Me, nude".

A virus must meet two criteria:

• It must execute itself. It will often place its own code in the path of execution of another program.
• It must replicate itself. For example, it may replace other executable files with a copy of the virus infected file. Viruses can infect desktop computers and network servers alike.

Computer Worms are viruses that reside in the active memory of a computer and duplicate themselves. They may send copies of themselves to other computers, such as through email or Internet Relay Chat (IRC).