DFU mode Device Firmware Update is a special mode where the device can still interface with iTunes. In DFU mode the screen will be totally black.
StealthBravo has sent a tweet showing how to put the Apple TV in DFU mode. You will be in dire need of this guide when the jailbreak tool is released, especially the new jailbreak would be throw a custom firmware, as the SHAtter exploit loaded on the PwnageTool to jailbreak the Apple TV 2G.
Requirements: microUSB cable
Steps to put Apple TV into DFU mode:
Step 1: Plugin your Apple TV to computer with microUSB.
Step 2: Hold menu + down button together for 6 secs to reboot.
Step 3: Once your Apple TV reboots immediately hold menu + play together until a message appears in iTunes telling you an Apple TV in recovery mode has been detected.