There is a new worm out there. It doesn't require you to read an email or open a file. Just not patch your machine.
If your machine is window 2000 or windows XP, and you haven't been updating your machine, you
might very well have been compromised by W32.Sasser.
Get the removal utility here.
Also after removal you'll have to enable your Firewall on your machine in order to go online and get the updates. If you don't,
well, you'll be infected probably before you get the change to update.