Your moderator has a compromised system and someone else gains access to your forum using their account. This results in a deletion rampage of content and other things. Likely not catastrophic damage but a pain for you to undo.
If you know your moderators rarely perform more than say 10 actions per day, you can set the add on to only allow them 10 actions per day. If they are compromised their mod powers end after 10 actions, so the mess is minimised.