OK. There's been another one of those worms going around again. This one is NOT spread by using email. It's spread by leaving your WinXP or Win2K box connected to the internet. If you get weird reboots, it's possible you need this...
http://securityresponse.symantec.com/avcenter/venc/data/w32.sasser.removal.tool.html
Someone wanna give it to Aaron?