Summary: http://www.trailfire.com/trailer/trailview/32338
Computer viruses are called viruses because they share some of the traits of biological viruses. A computer virus passes from computer to computer like a biological virus passes from person to person.
There are similarities at a deeper level, as well. A computer virus must piggyback on top of some other program or document in order to get executed. Once it is running, it is then able to infect other programs or documents. Obviously, the analogy between computer and biological viruses stretches things a bit, but there are enough similarities that the name sticks.
Once a virus is on your computer, its type or the method it used to get there is not as important as removing it and preventing further infection. So it is important to prevent a virus from entering your system and spoiling it.
