You can read about it http://www.pcworld.com/article/228174/new_xbox_firmware_bricks_some_consoles_microsoft_makes_amends.html. Get this though they're actually replacing the affected units for FREE!! With a brand spanking new xbox 360s model with a 250GB HDD.
Personally I'm actually hoping it messes up my old one (never thought I'd say that lol) even though I have another new 360s already.
edit: found a better article
