This is my work machine doing this, by the way. Fricking annoying -- work for hours on stuff and then Poof! it's gone.

It's not a virus. I've checked it numerous times, each time with the latest and greatest updated signatures. Additionally, it's been doing this since before the existence of Blaster or Sobig.F.

A friend thinks it's hardware. I guess I get to call our PCHelp people tomorrow to see what's up.