Before you can hope to protect yourself from something you must know what it is. What is a virus? In it’s most simple terms, a virus is something that “copies” itself.
Unfortunately, that’s not all that viruses do. They also usually include a ‘payload’ of a destructive and/or harmful factor that is used explicitly to either get attention or just release angst from the virus author. You see, unlike biological viruses, there is no way for a computer virus to evolve on it’s own. As such, they are all manmade, and though some of the functions of specific viruses were created accidentally, their distribution and propagation is now deliberate in every way.
A Trojan Horse or Trojan, like the wooden horse in greek legend, lives up to it’s namesake. Trojans are designed specifically to gain access to a computer that the author or distributor would not have access to through otherwise trusted means. They can be used to remotely control a computer for various nefarious purposes or simply to provide logs of every key pressed and all Internet sites visited.
Worms are viruses that propagate across a network by attacking a computer through vulnerable software and services exposed to the network. Since the Internet is the largest network in existence, it’s also quite a busy place for Worms.