I guess, in time, you would need to run your Antivirus on hardware too to check for malicious code. I guess it would be an expensive exploit, nonetheless it could be exploiting hardware and storing itself in your hardware’s firmware.

A good practice from now is to buy reliable manufacturer’s hardware and update your firmware when they become available.

News excerpt from http://news.com.com/PC+hardware+can+pose+rootkit+threat/2100-7349_3-6162924.html
ARLINGTON, Va.–PC hardware components can provide a way for hackers to sneak malicious code onto a computer, a security researcher warned Wednesday. Every component in a PC, such as graphics cards, DVD drives and batteries, has some memory space for the software that runs it, called firmware. Miscreants could use this space to hide malicious code that would load the next time the PC boots, John Heasman, research director at NGS Software, said in a presentation at this week’s Black Hat DC event here.