Virus-like program that spreads automatically to other computers by sending itself out by email or by any other means. A program that propagates itself by attacking other machines and copying itself to the affected machine.
Worms have self-replicating code that travels from machine to machine by various means. A worms first objective is merely propagation. Worms can be destructive depending on what payload they have been given. Worms may replace files, but do not insert themselves into files.
This is a worm that travels through Windows Live Messenger in order to infect other users. It spams other windows live messenger accounts without the infected user ever knowing. The package that is installed gives the attacker the ability to remotely execute code using the Print Spooler Service Vulnerability.