Ok , Many of you are working on the married eeprom and hdd , I must admit this looks like the most valid explanation around so far .
I have started to look at this from another angle .
WHAT DOES MICRO$OFT GET OUT OF THIS

Point :- Well as we all know Micro$oft is big on the fight against piracy but really did this ban stop piracy ?
A :- NO We all know not to use copied games on Xbox live.
Point :- To stop cheating on Xbox live?
A :- IMHO Yes I think this ban has done this (for now) , As many people are removing mods and putting back there stock drive.
Point :- To increase the sale of Xboxes ?
A :- YES !!! Just look at the timing !! Just when Halo 2 comes out so many boxes banned. And I know of loads of people who went out to buy a new Xbox to get back online .
So looking at this I feel that Micro$oft is scanning for known game cheats (trainers) And I know If you use Slayer Auto Installer (Great Program Lads

) It installs a bunch of Trainers .
Thoughts on this please ..
Thanks to all who are trying to find out what Micro$oft are doing
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Ps . Please also be aware that Micro$oft keep an eye on this forum