Samuel King and colleagues at the University of Illinois at Urbana-Champaign have shown that they could gain control of a computer by <A HREF="http://www.lockergnome.com/news/2008/04/30/hackers-learn-to-threaten-computer-hardware/">adding malicious circuits to its processor.</A> Because these circuits interfere with the computer at a deeper level than a virus, they effectively operate "below the radar" of AV software.

To evaluate the risk from such hardware, King's team designed their own malicious circuits. They used a processor called a field programmable gate array (FPGA), whose logic circuits can be rearranged, to create a replica of an existing open source processor called Leon3, which contains around 1.7 million circuits. They then added about 1000 malicious circuits not present in Leon3.

The team found that the circuits allowed them to bypass security controls on Leon3 in a similar way to how a virus hands control of a computer to a hacker, but without requiring a flaw in a software application. When they hooked the FPGA up to another computer, they were able to steal passwords stored in its memory and install malicious software that would allow the operating system it was running to be remotely controlled.