Seems like Microsoft claims they can detect illegitimate copies of Halo 3: ODST. Xbox Live Chief of Police Stephen Toulouse told kotaku.com:
I can be clear however that this applies to illegitimate copies only, the ban covers the Xbox LIVE account and could possibly include their console depending on the results of our investigations (which are ongoing). We do this from time to time with titles to combat piracy.
If a user happens to purchase a legit copy of Halo 3: ODST early, then our problem is not with the user but the retailer who broke the street date. Those individuals will not be punished.