UEFI is used as a replacement to old BIOS of windows. BIOS prepare the base for loading the entire operating system, but it does not apply any malware related security check in the pre-OS environment. Thus, it is very easy, for the boot sector viruses to ditch BIOS and affects the boot sector of the system.
Once the boot sector is affected, the virus becomes immune, and it becomes undetectable to any antivirus installed in the system. Such viruses do not go away even if the system is formatted, since they reside in the boot sector. When the new Operating system is installed, once again they are ready to show their evil effects. With UEFI, system is immune from boot sector viruses. This is because, UEFI comes with some valid public keys. If the boot loader of a particular vendor is signed with a private key that matches with a public key of UEFI, it is allowed otherwise it is blocked.
Also read Cross Computer Password Syncing in Windows 8 reviewed by us.
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Thus, due to the increased security of windows 8 boot sector, there are very strong chances that hackers may shift their attention and start targeting the hardware directly. The news comes directly from McAfee in their threat predictions for year 2012.