In addition to this morning’s release ofiOS 6.1.3, Apple has also seeded a new version of its Apple TV software. The update brings the firmware to version 5.2.1, and it includes a number of bug fixes as well as support for thenew Hulu Plus app.
Unfortunately, as with iOS 6.1.3, the bug fixes are actually patches for the exploits used in the latestevasi0n jailbreak. So if your Apple TV isjailbroken, or you would like it to be in the future, you’ll want to be sure to stay away from this update…

As noted byMacRumors, Apple has posted anew support pagedetailing the security content of today’s Apple TV 5.2.1 release, where it names off 3 bugs that are all clearly related to the evasi0n jailbreak, as Apple credits theevad3rsfor discovery.
Here’s one of the exploits mentioned:
Available for: Apple TV 2nd generation and later
Impact: A local user may be able to execute unsigned code
Description: A state management issue existed in the handling of Mach-O executable files with overlapping segments. This issue was addressed by refusing to load an executable with overlapping segments.
Unfortunately, Hulu Plus users that want access to the new app, but don’t want to lose their jailbreak are caught between a rock and a hard place. Because from the sound of it, you have to update to iOS 5.2.1 to get the new app, which will kill the hack.
At any rate, folks who don’t care about preserving their jailbreak can get the new version of the Apple TV firmware by visiting Settings > General > Update Software on their ATV set-top boxes, or you’re able to grab the whole thing from ourDownloads page.
Jailbreakers, you’ll just have to stay tuned until we get more information.