As posted earlier, there is a file on the Xboxhacker.net forums that is supposed to run Linux on an unmodified box usin the Microsoft game "Mech Assault". We can now confirm that it works - there seem to be quite some more vulnerable games out there!

You can do the same trick as with the 007linux exploit (memory stick or swapped hard disk with the hacked savegame and the Xbox-Linux-signed bootloader XBE), and you'll get the Item "Run Linux" when loading a savegame.

Using the key published on Xboxhacker.net earlier, everyone can sign their Xbox Linux bootloader themselves now and run it on an unmodified box either using the game "007 Agent Under Fire" or "Mech Assault".