The Hypervisor in Microsoft Xbox 360 kernel 4532 and 4548 allows attackers with physical access to force execution of the hypervisor syscall with a certain register set, which bypasses intended code protection.
http://www.securityfocus.com/bid/22745
http://www.securityfocus.com/archive/1/463974/100/200/threaded
http://www.securityfocus.com/archive/1/461489/100/0/threaded