"Because the data looked like typical DNS traffic it wouldn't be detected or logged by firewalls or intrusion detection systems. He also pointed out that monitoring DNS could help in other unrelated ways: because the recent MSBlast worm did lookups on windowsupdate.com infected machines could have been detected by simply monitoring DNS server logs."
Iphtashu Fitz writes "Without DNS the internet wouldn't be all that useful. Despite being a ubiquitous part of the internet it is overlooked by many as a potential security hole. At this weekends Defcon 12 conference in Las Vegas, security researcher Dan Kaminsky warned that DNS can open up seemingly secure networks to attack. Because most firewalls and other security devices treat DNS requests as harmless it provides an excellent conduit for transferring covert data in and out of otherwise protected systems. At Defcon, Kaminsky demonstrated some software that allows a server to act as a communications hub using DNS. This let him transmit instant messages and even audio streams over an encrypted connection carried by spoofed DNS requests."