Uhm, when i was leaving a "special" app on and left my pc for a while. I didn't knew that it made my computer crash after 15 min. I came back and everything was... uhm... blank. I donno what happend but i had to chmod all my files back to get permission to my pc since it locked all my files. And no it wasn't a virus, just some stupid lame hdd crash.
EDIT: Yuk, seems like i've allready posted in this topic. Owell, my worst day just happend a week ago.