Windows Live Messenger Virus
You'll no doubt hear this from a lot of sources, but if you see this popup from one of your friends.. DO NOT CLICK ON IT.

It's a nasty virus that will take a lot of work to remove.
I clicked on it, but I was lucky - because I run enough programs like XP SP2, Defender and VirusScan. One of these popped up a little warning box and nothing happened. I should have known better - but it proves how "social hacking" is so much more effective. I would never have clicked on an email like this, but an IM from someone I know? Clicked without a second thought...scary.
BTW, how do you know if you got it? Trust me, you'll know. This is not a stealthy keylogger. This thing will open a million windows running all sorts of nasty commands.
You'll know.