Let's be clear: the only reason a new Apple TV hadn't been jailbroken yet is that new Apple TVs hadn't shipped yet; the Dev Team hackers figured out how to do it days ago. Here's how it was done.
Turns out the SHAtter exploit that sprung the fourth-generation iPod Touch also—not totally surprisingly, since they're both iOS devices—works on Apple TV 2G. You've got exactly one app to choose from at the moment, that being the native Lowtide. But it's only a matter of time until developers start creating for Apple TV.
As always, proceed with caution! Especially since the current benefits to having a jailbroken Apple TV are pretty much nil, and will stay that way until we see some juicy app action. [Dev Team]