The FireCore developers (the same guys behind aTV Flash) have released a jailbreak tool for the Apple TV 2nd generation called “Seas0nPass”. This jailbreak tool, like the popular Pwnage Tool app, can create a custom firmware file for the device to load and install non-Apple approved apps. Seas0nPass has been created exclusively for the Apple TV and also comes with an option to perform an easy “tethered boot” – a procedure that requires you to boot the Apple TV plugged in your computer. Seas0nPass lets you do that with a few clicks, in a simple and minimal user interface.
To use Seas0nPass, Mac OS X 10.6 is required. A Windows version will come out soon and, again, this only works on the 2nd gen Apple TV – don’t try to use with any other iOS device. Seas0nPass is free and open source, you can download the source code here. For instructions on how to use the app to jailbreak your Apple TV, see here.