This is an interesting question. With computer viruses and worms becoming widespread, they have gained quite some attention over the past years.

Computer security experts have come up with the terms computer virus and worms, because they infect computers and can make them "sick" similar to how real viruses can make your body sick. Similar to nature, computer viruses and worms have a replication mechanism, that means they have the ability to spread and infect new computers.

A virus is a computer program that replicates by attaching itself to another object. For example, a virus could be hidden in a Word document. When you give that Word document to a friend (via disk or via e-mail) you have spread that virus. If your friend opens that Word document on her computer it can then infect other documents, or if it is a malicious virus might even delete some important files.

A worm is a computer program that replicates independently by sending itself to other systems. Thus a worm can spread much faster. Worms often spread over e-mail. When worms are received through e-mail, they often look at the address book and automatically send a message containing the worm to everybody in that address book (including your friends). Again, if that worm is malicious it might delete files.

Viruses and worms are written by hackers that want to play around or intentionally do damage to computers. The best way to prevent getting infected by a computer virus or worm is to run virus detection software on your computer. This will scan for viruses and eliminate them.