KindMind writes: The Register has a story on a researcher that has developed a network card firmware based rootkit. From the story: Guillaume Delugré, a reverse engineer at French security firm Sogeti ESEC, was able to develop proof-of-concept code after studying the firmware from Broadcom Ethernet NetExtreme PCI Ethernet cards
... Using the knowledge gained from this process, Delugré was able to develop custom firmware code and flash the device so that his proof-of-concept code ran on the CPU of the network card. You can read more on his blog.