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]