A 20 minute CERT podcast on botnets gives an overview of botnets - sizeable networks of compromised computers remotely controlled by hackers, used for stealing data, identity theft, hacking other systems and spamming. Hear how compromises occur, how botnets are used and controlled by the black hats, and how to secure your systems to avoid compromise and clean out bot infections.
If you don't have audio facilities on your system, or simply prefer to read, a transcript is also available.
A little collection of information security-related podcasts from CERT. They are aimed at busy executives with largely nontechnical content.