What is a Worm?
A worm is the same as a virus but with these differences:
- It doesn't need a host to attach to, it's stand-alone
- It spreads using network connections (a virus only infects local files)
- It can contain other malicious code such as a Trojan Horse or backdoor
You get a worm the same way you get other malware, bad protection or unsafe surfing, to remove one, go here. And to prevent problems in the future go here.