A software update for the Xbox 360 makes it harder for users to install alternative operating systems such as Linux or run other non-Microsoft software.

Like most console manufacturers, Microsoft is believed to sell Xbox 360 consoles below cost, making up the difference on game sales. But this only works if they can be sure that only 'authorised' software will run.

Consequently, manufacturers design in various mechanisms to prevent the use of software from other sources. In the case of the Xbox 360, this includes signing all code with Microsoft's private key.

But enthusiasts discovered a way of tricking the Xbox 360 hypervisor into executing unsigned code with full access to the hardware.

Microsoft's January update to the Xbox 360 operating system update - delivered via Xbox Live and the Xbox web site - patches the 'vulnerability' that let the method work.