MyBitcoin having been a scam was obvious, but it's good to finally remove all doubt. If MyBitcoin really had been hacked, there wouldn't be any old coins stored in their receiving addresses; they would've either been transferred to a different address by the attacker, or transferred to a different address by MyBitcoin's operator, a long time ago. Unfortunately, this transaction probably involves coins being sent to a coin-mixing service, rather than directly to something linked to an identity.

(Also interesting: those addresses weren't completely cleaned out; they still have a few coins in them, after the recent withdrawals.)