UEFI is the "more better" replacement for the traditional system BIOS, and is appearing on newer motherboards and is supported by the latest operating systems such as Windows 8. Italian researchers have discovered that it is possible to insert custom code at boot time (a bootkit) and thereafter perform all kinds of naughty stuff on the operating system with impunity. They also indicate that it should be possible to use this type of exploit on OS X and Linux systems that support UEFI. How nice. They have a pretty detailed look at the issue at the link below. Note the English grammar is a little shaky in parts, due to the Italian source.