So, what makes Windows 8 more secure? Perhaps the biggest security feature of Windows 8 is really not a Microsoft or Windows 8 thing at all: UEFI (Unified Extensible Firmware Interface). UEFI is an open standard used to replace the archaic BIOS typically found on PC hardware.
UEFI has been around for a while, but systems built for Windows 8 (and Windows Server 2012) are the first to take advantage of the feature of UEFI that allows for pre-boot authentication. Basically, UEFI will only allow software with recognized, valid security certificates to run, so it prevents rootkits or other malware that might attempt to load at boot from doing so.