There's a worm, the Conficker Worm, that's supposed to activate itself tomorrow, April 1st and raise hell.
If you can't get to the Windows Update site, you probably have it. If you can get to the Windows Update Site. Make sure you're updated.
Malicious Software Removal Tool from MS will get rid of it:
If you can't load that URL, then you probably have the virus. It is a particularly well designed turd and will infect computers throughout your lan if it gets into one of them.
Use a linux live CD or an uninfected computer to retrieve the MSRT if you are goobered.
If you know who the responsible hackers are, Microsoft will give you $250,000 to rat them out.