Windows 8 is being touted as the most secure version of Windows ever. The way that Windows 8 client machines will boot is going to be quite different from the way that current Windows PCs do. Instead of a BIOS, Windows 8 PCs will include an implementation of UEFI (Unified Extensible Firmware Interface) The move to UEFI and secure boot is one of the results of that effort. The impetus for this change is that attackers have become proficient in recent years at finding methods to load malware into the BIOS and firmware that underlie the OS.
Source: https://threatpost.com/secure-boot-windows-8-worries-researchers-092211/75679/