The biggest problem is if you have been using a standard password in the beginning as had the machine accessible globally via internet.
You will have to reset to factory settings as most probably you have malware on it.
Hi - The ORIGINAL SD Card with MinePeon installed did have the default password. Once I was hacked (the first time) - I switched out an ENTIRELY NEW SD Card with MinePeon reinstalled -- with a VERY secure password (25 char+) -- The Hacker is back -- and seems to have broken that one too.
He hasn't broken it, he's just found another way in. He could have modified something in the OS, maybe a command that you are using that executes something that gives him access.