THIS IS FROM BUNGIES SITE
Autoupdate 4: Q&A
Tomorrow, Wednesday the 20th of July, we will release Autoupdate 4. This is a small file that updates your version of Halo 2 to address various issues. It only takes a moment to download the file, but it is required for continued play on Xbox Live. If you do not wish to download the file, that is your choice, however, you will not be able to play Halo 2 on the Live service.So you've been warned. Read on for lots of specific info.
Q: What will happen to a player if his or her Xbox contains modded content?
A: You will be banned if you are detected playing our game with modified Halo 2 content. Your ban will be from matchmaking, it will be permanent, and there will be no appeal process.
So it looks like it's just banning modded Halo 2 content....WAHOO!