Apple has released a software update for the third-generation Apple TV. It's available as an over-the-air download on the set-top box, and can be found by going to Settings > General > Software Updates. It appears to be a minor update, likely containing bug fixes and performance improvements.
The third-generation Apple TV was first released in early 2012. It was the first verison of the Apple TV to support 1080p video content, and is still sold for $69 alongside Apple's most recent set-top box, the fourth-generation Apple TV.