Kon-Boot

Kon-Boot is an prototype piece of software which allows to change contents of a linux kernel (and now Windows kernel also) on the fly (while booting). In the current compilation state it allows to log into a linux system as 'root' user without typing the correct password or to elevate privileges from current user to root. For Windows systems it allows to enter any password protected profile without any knowledge of the password.
http://www.piotrbania.com/all/kon-boot/