How to Jailbreak Your Apple TV 2G Using Greenpois0n (Mac)
These are instructions on how to perform an untethered jailbreak on your iOS 4.2.1 Apple TV using Greenpois0n for Mac.
Open your web browser of choice and navigate to http://www.greenpois0n.com. Click the Mac link at the bottom of the screen.
When prompted save the download to your desktop
Double click the downloaded zip file to extract it then double click the extracted greenpois0n file to launch the application
When asked if you are jailbreaking the Apple TV click Yes.
Disconnect your Apple TV from the power and USB then click the large Jailbreak button
You will now be instructed on how to place your Apple TV into DFU mode.
Connect the USB cable immediately.
After 7 seconds connect the power cable.
Press the Menu and Play/Pause buttons for 7 seconds
Release the buttons.
Once your Apple TV is successfully in DFU mode jailbreaking will begin.
Once the jailbreak is complete you can press the Complete button. Make sure to wait 40 seconds before disconnecting the USB cable so the jailbreak process can finish up on the device.
***A big thanks goes everyone who made this jailbreak possible.