Viruses, Worms and Trojans

What is a virus, worm or Trojan horse?

Malicious programs come with all kinds of funny names. You have probably heard of viruses, but what are worms and Trojan horses? These programs have different characteristics and operate in different ways. They can also be combined with each other blurring their distinctions.

Virus
A virus is defined as computer code that can spread by making copies of itself. Typically, the virus does this by inserting itself into another program, called a host. A virus cannot exist without a host.

Worm
A worm is a complete program that isn't dependent on another program. Think of it as a standalone virus.

Trojan Horse
A Trojan horse is a malicious program that disguises itself as something benign. Typically, it is downloaded by the user thinking that it is something else.

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