A computer worm is a malicious program that can replicate and run itself. It differs from a computer virus in that it doesn’t need to embed itself into a host program to run. Computer worms usually spread through networks, although other methods of transport can be utilized such as local drives.
Definition from About.com
Worms - A worm is a small piece of software that uses computer networks and security holes to replicate itself. A copy of the worm scans the network for another machine that has a specific security hole. It copies itself to the new machine using the security hole, and then starts replicating from there, as well.
Definition from Howstuffworks.com
