Essentially, the BIOS is the instruction set given to the computer before the operating system has loaded -- which also means long before any anti-malware software is protecting the system.
According to the researchers, they insert a small piece of code into the BIOS, and they get complete control of the machine. Most disturbing: the code inserted in the BIOS will survive through re-boots, hard-drive wipes, and attempts at reflashing the BIOS. Ortega and Sacco demonstrated successful attacks on Windows, OpenBSD, and on an OS within WMware Player.
From an entry at the ThreatPost blog:
"It was very easy. We can put the code wherever we want," said Ortega. "We're not using a vulnerability in any way. I'm not sure if you understand the impact of this. We can reinfect the BIOS every time it reboots."
The good news is an attacker needs to have a machine where they have "root" privileges, or they need physical access to a machine. While this attack won't be prevalent over the Internet: would you know if the BIOS in one the machines on your corporate network was altered, and infected in a way that no traditional firewall or antimalware application would pickup?