Once the server I was using caught a bug. One of those bugs from a hole in apache or php, I don't remember which. Every index.* was changed to be on that said something along the line of "surprise, you've been hacked". I spent days fixing index pages and looking for malicious redirects. Not so fun. I always worry about Facebook and Twitter that they might be victim of a leak like that, and who the heck is Linkedin anyway? I got an account but I'm not sure why.
*bawl* I missed the karma.