dude, nothing has been confirmed at all. and the actual most LEGITIMATE theory is not even the one you posted a link to. the most legitimate one is the "marriage" theory. go on xbox-scene and find it yourself, i'm not posting the explanation myself.
i have been on xbox live fine the past 2 months w/my mod chip turned off. I have been playing Halo 2 the past days nonstop when at home. I am still on xbox live just fine. if they ban me from xbox live, i'm just going to go buy another xbox to use for live solely.
and for the record, this is quoted from the xbox live user agreement:
"Xbox Live may only be accessed with an unmodified, except for Microsoft-authorized repairs and upgrades, Xbox video game console. Any attempt to disassemble, decompile, create derivative works of, reverse engineer, modify, further sublicense, distribute or use for other purposes either the hardware or software of this system, is strictly prohibited and may result in termination of your account and/or your ability to access Xbox Live."
EDIT: and this "banning" stuff has been going on since mid october, well before Halo 2 was released. Go scan the xbox-scene forums and you will see. it has nothing to do with halo 2, but rather with the recent upgrades to the xbox live service. The reason people are thinking it has to do with Halo 2 is because the first time you go on xbox live with halo 2, you MUST download an update for xbox live. Which means people who haven't updated since early october will now have this new upgrade.
okay ill explain the marriage theory because i know people on here are lazy
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The marriage theory basically says when you FIRST sign up with xbox live, the service links your EEPROM (xbox serial #) to the Hard drive serial # (basically "marrying" them). And say you get banned for going online with your modchip turned on. The ONLY way to get back on is to get a new EEPROM (you can get them online for like $5 from people, i'm not going into detail as to how you do the actual replacement of it).
If you read people's posts who have been banned and have been on with a new EEPROM, they usually last for about 10 hours or so, then they are banned again. This is because the "marriage" has been broken (xbox live is seeing your HD serial # with a new EEPROM #).
So that is the most recent, logical, theory that people are talking about being the source of this. So basically if you get banned from xbox live, the only way to get back on is to get a new HD and a new EEPROM. So basically its easier to just get a new xbox solely for xbox live use.
If they were doing LPC scans, this means my xbox would too be banned since I have a modchip on there. However, on a v1.6 xbox, the LPC needs to be rebuilt when installing a chip (connecting other points to the LPC points via soldering wires between them), and an LPC scan on these would definitely pick up something not right since there are closed circuits where there shouldn't be.