So far, what is known to me is that UEFI boot is not very secure. There's a few reasons why, and various tests have been done for proof of concept. A team of security researchers at ITSEC were able to create what they called a "UEFI bootkit" and this was designed to specifically blast Windows 8. What makes this flaw a big issue in my opinion is it's ability to bypass the PatchGuard (kernel patch protection) and Driver Signature Enforcement policies in the Windows kernel, and can overwrite the original UEFI bootloader. [media=youtube]xKgz4Y_sNjo[/media]