My question really is what exactly did they hacked that made it necessary to shut down the online servers?
Got on as MODs. Shut down to keep them from getting on as other users as well, and also to prevent them from incorrectly using mod powers.
So they hacked it through the use of a in-game modification on the hacker's end?
No, MODs as in Moderators.
Oh. So he hacked into one of the moderator accounts and shut it down?
It's somewhere on the forums, but now it requires a lot of digging to find, so to sum it up: multiple people got into a couple moderator accounts, messed around with stuff, didn't shut it down but caused panic/confusion, they posted links to frame other sites (frame for lack of a better word), and they (people in charge of the game, not the hackers) had to shut down servers to keep everyone else safe/stop confusion.