What happen? Is this the result now of centralized exchange? or just weak on the security breach?
That's why I'd always choose reputed exchange to avoid a possible problem in the future.
It seems there's a bug in the balance of users. Somehow users were able to get the balance that they never had to begin with. Seems like Exlly uses OpenTrade as their exchange template and got screwed. There seem to be many cases that exchange who uses OpenTrade code got this error/bug/hack whatever you named it.
Any other exchange that use OpenTrade as their template/main software should be vulnerable for this bug.