Lol...the domain didn't get fucking hacked!!!
The domain was free!! We closed it after we made a new one!! Then they registered this. Therefore it didn't get fucking hacked!!! How much times do I have to tell?
Lockabe
Seems like you fell victim to what's called a session hijacking attack. Someone can't really, magically just remotely auto-complete and login to your account it must've happened through HTTP cookie theft. Which means the hacker used a webserver with a cookie catcher to store cookies from remote machines. Thereby the hacker assumably used that cookie in combination with a uhm... I think the hacker used a cookie manipulation tool or what not. Else I am not sure what possibly could've happened. Seriously I'm clueless... really. A good counter-measure to help protect against session hijacking is though to use the socalled Noscript add-on for Mozilla Firefox, if you use another browser don't be sad simply just find a similar web-script & web-object blocker and use that. However I recommend Noscript at all costs for now. It will definitely prevent the cause of any potential account session hijacking. Good luck.
Go here to read more how to protect against threats. It's been my help resource for a while.