Not sure if this is really much help but I've heard a few people say their groups have randomly been disbanded and heard that it's most likely a glitch and not a hacker. Now I'm not saying that it isn't, just saying another possibility on what it could be before we jump to such conclusions.
IT could very well have been someone that has had access to those accounts as well. As for personal accounts, are you sure you didn't share any of your log in information with anyone?