I had theorized at one point in the past that it was possible for MS to be pulling information, or running modchip checks on your system without your knowledge and without logging on to Live. Several people shot this idea down, and in a thread about the 2.0 update one eventually convinced people into updating to Live 2.0 because he claimed he "knew" it was safe, even for those with modchips.
Well in answer to this I have included a link to an article on the XBox Linux site that demonstrates that with at least one game MS IS collecting info about your XBox, even if not logged into live. It also shows that it is quite possible to communicate with the live servers without logging on.
I am not saying that MS is doing anything with this info, but it is quite clear that they could potentially detect you modchip even without logging on to live. They just aren't doing anything about it yet.
My advice is to block all traffic from your XBox when you have your chip enabled, or unplug the network line.
Xbox Phones HomeMorden.