Consequences of stealing items in mmos

[Istjawitzig]

I've been wondering about something. For example, let's say someone leaked usernames and passwords of some account on some mmo. Then is someone else finds the leak and accesses those accounts and steals some/all items from that account, is it possible for the game company behind the mmo to sue or take any legal action against that person? And is so, has it ever happened to anyone? I mean you would be using public information, so is it illegal?