The back-corner forums where console modding enthusiasts and/or software pirates get their max-and-relax on have been abuzz for a few days now over a new wave of Xbox 360 bans coming down the wire through Xbox Live. Microsoft does this periodically, because, unsurprisingly, they ain't down with modified consoles and the piracy it enables.
Normally I'd be all pro-mod or whatever, but since there isn't really any sort of homebrew scene on the 360 to justify all that firmware hacking, there isn't much of a good reason to mod your console in the first place. So, if you've been using a modified console online, there's a chance that your system has been banned and won't be able to connect to Xbox Live anymore. Which, really, serves you right for connecting to Live with a modded system in the first place, ya big dope.