A SecurityFocus article picks up on the possibility of rootkits in the computer's BIOS. The same principle applies to rootkits in video BIOS and network card BIOS. The thing about these locations is that a reboot won't clear them, nor will a normal complete system rebuild - not even a new hard drive will clear them ... unless, that is, the code in the BIOS is just a stub, a loader for the main payload on disk. Given that the machine BIOS, by its very nature, gives low level access to the hardware, it is conceivable that a stub could load the remainder from another BIOS store, or from a normally inaccessible area on disk (such as a sector marked bad).
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