It is really difficult to pick my worst disaster. I've had so many of them. I've reinstalled Windows more times than I can count. Luckily for me, I back up all data, so I lose nothing but time. But if I had to pick one, it would be the time I found adware on one of our MS Exchange servers (this server had about 6k mailboxes on it). That was bad, logging into a server only to find popups. I didn't know who I was more upset at, MS or the moron who was surfing the web from the server. I won't go into the rest.

I actually rebuilt my Windows machine two days ago. I couldn't boot into it. Instead of fussing with it, I decided to rebuild since I was on that same build for about 6 months. Knoppix was able to transfer important files from the Windows partition to my jump drive.