How to secure your BIOS
You probably don't interact with your PC's BIOS (Basic Input/Output Operating System) much, but it occupies a unique and highly privileged position in your computer's architecture. Since the BIOS loads before the operating system–and before you enter your user credentials–malware surreptitiously introduced into the BIOS could activate itself long before any anti-malware software has an opportunity to detect it. A sophisticated and malicious program operating at such a low level could take control of your PC without providing a clue that it was there.
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Story added 7. April 2012, content source with full text you can find at link above.