There is a worm currently running around. It affects XP and Win2K.
You can check for, remove, and inoculate against it using Microsoft's website

http://www.microsoft.com/security/incident/sasser.asp

I know all too well.. I've literally spent all weekend trying to clean my computer and get rid of this nasty thing. I don't even think it's Sasser anymore because I've scanned and there's nothing.. nevertheless there's something there that's causing me much anguish. On the bright side of things, I have a fresh installation of XP Pro as a result!

First line of defense which should've helped against this would've
been a firewall. A good one would've blocked access to the ports
the Sasser virus is using.

I had to turn off my firewall for about half an hour a few days ago, and I had to spend the whole sunday cleaning this stuff...

So, FIREWALL for me, is as important (or more?) than antivirus, which by the way only 1 of three I used, was able to find the sasser on my machine.

I've never killed anyone with my bare hands, but I've never been in the same room as someone that programs viruses.

Check out this site for Sasser removal tools. I got hit too.

http://sarc.com/avcenter/venc/data/w32.sasser.removal.tool.html

<<<-- Originally posted by Dylan Couper : I've never killed anyone with my bare hands, but I've never been in the same room as someone that programs viruses. -->>>

I wouldn´t stain my hands... I ´d rather use the keyboard... and maybe make them choke on the mouse.

The first line of defense is actually good ol' fashioned Windows Update. 99% of these viruses will be completely harmless to you if you just make a note to keep using Windows Update. It's easy as pie, and you can even set it to automatically install Critical Updates without even telling you.

And, of course, keep your virus definitions up to date too...

Sasser is completely harmless to a properly updated OS.

Agreed. And get a firewall. They are cheap.