Xbox Live mandatory update is for wireless adapter WPA2 support
If you have yet to fire up your Xbox 360 today, when you do, please be advised that message noting a mandatory system update will greet you.
Should you go online, that is.
Anyway, don't get too excited. You won't be Tweeting or Facebooking afterward - it's just an update for the wireless adapter.
If you plan on getting the new 802.11N wireless adapter next month, you'll need this update.
More through through the Major.