What do I do if I get hacked???

I was pretty surprised when in one of my games (319095) I found some comments offensive to other players in the chat that were coming from ME!
I couldn't understand what had happened, and the next thing I knew: HE WAS MESSING WITH MY FEEDBACK AND MY IGNORE LIST!!!!!!!!!!!!! I already changed my password, but I'm afraid it might happen again. What the HELL would I do? Please tell me, I don't wanna be remembering eighty passwords.
