If you haven't already heard about Conficker, where have you been?
Get to and check your home PC before April 01 rolls around.
If you can download the MS patch, do so.
For others, with special *cough* versions *splutter* of MS software, at least disable AutoRun in MS Windows (something everyone can and should do regardless of the provenance of your software ).
The United States Computer Emergency Readiness Team (US-CERT) have put together the essentials for corporates and home users:
Check your PC
Disable AutoRun is outlined at point III under the solutions link.
Go on! Why are you still here?!