Someone keeps deleting my Youtube Videos!?

About three days ago i posted a clip from Saturday Night Live and it turned out to be very popular, it had about 100,000 views. The next day i log into my youtube account and i have a message from a user named "YTScreener088" saying that they deleted my videos. i go into my videos and they are all deleted?! i could kind of get that they would have deleted the SNL clip, but all of the other videos were homeade.heres a link to their account http://www.youtube.com/user/YTScreener80 i really dont think that this user is a memeber of the youtube staff and when i clicked on my deleted videos it says "video deleted by user" so they must have hacked into my account!!!! why!