The enemy in the network card
Security expert Guillaume Delugré, who works for the Sogeti European Security Expertise Center (ESEC), has demonstrated that a rootkit doesn't necessarily have to infest a computer. The expert used freely available tools and documentation to develop custom firmware for Broadcom's NetExtreme network controller. He was then able to conceal a rootkit within the firmware, making it untraceable by the virus scanners usually installed on a PC.
You don't need to be a genius to debug a pf.conf firewall ruleset, you just need the guts to run tcpdump