Microsoft has used data gathered by by the Crackdown Halo 3 beta downloads to start a purge of modded machines from Xbox Live.
One of the problems with the most popular firmware hack is that it is detectable unless either the Xbox 360 kernel or the game code signing are thoroughly hacked.
According to Xboxic Microsoft's Spring Update and the Crackdown title update or the Halo 3 beta code itself cooperate to determine that the firmware has been modified.
Microsoft’s has posted the following note on the Gamerscore Blog which says that some consumers that try to login to LIVE who we detect have illegally modified their console will get an error code (Status Code: Z: 8015 - 190D) when trying to connect to the service.
They will not have their account automatically banned from LIVE, but they will no longer be able to access the service from the console they modified.