The update to version 4.2.1 addresses an issue where some viewers may have experienced a screen flicker, where the box would fail to wake up once it had done to sleep (we know the feeling), and where some users may have noticed an absence of sound.
The patch, which can be downloaded over-the-air from the Apple TV box Settings menu, also fixes some other stability issues.
For more on Apple TV, see our UK Apple TV Review page