There are those people who just call everything a virus and there are those that think they know exactly what type of malware their infected with. Well, Im here to clarify between the three.

Viruses

A virus is made simply to cause damage to a person's PC. They usually bind themselves to all your files making them hard to remove. Viruses are made to leave your PC unrepairable and you will need to format if your anti-virus doesn't catch it in time. That's why it's so important to have good anti-virus software.

Worms

A worm is similar to a virus but sometimes isn't made simply to cause damage. Most of the time a worm is made to collect personal information, to sell or use for identity theft fraud later. Worms use your PC to automatically hack other PCs or use other hacking tactics like mailing a attachment of the worm to all your contacts in your email list(s).

Trojans

Trojans are often times called zombies, bots, or backdoors, but they fall under the same category as trojans. They both are made to give a hacker easy remote access to your PC anytime he or she wants. Sometime's the hacker will install password stealing key loggers, and steal your installed software's cd-key (including your Windows key).