The SHAtter exploit was used on an iPod touch to decrypt the AppleTV firmware.
The AppleTV device has not yet been exploited - although it is likely susceptible to the same exploit. Once hackers get their hands on the device, they can try to use the exploit, then try to run jailbroken firmware on it.
At this point, without knowing details of the SHAtter exploit, it's unclear to me whether/not that particular piece of code comes into play during a normal firmware update (since we don't know how the mini-USB port can be used yet - presumably "normal" code updates are done via wifi/Ethernet).
