“ACCORDING TO REPORTS, Microsoft has started automatically updating Xbox game consoles with a new version of the Dashboard software. When users use “Xbox-Live”, the feature of the Xbox that lets you play against other people on the Internet, the Xbox will also download some bug fixes without asking you.
The Xbox games do have a warning on them that connecting to the Xbox Live Vole Service may update your Xbox, however.

The particular bug that this update will correct for the user is the ability to run Linux. Once the update is in place you will not be able to install Linux on your Xbox any more, at least not in the convenient way that the Dashboard bug allowed, according to the XboxLinux pages.”