A lot of activity is going on in the area of botnets. If you’re curious about them, you can study a few key references.
An Inside Look at Botnets. Paul Barford. Vinod Yegneswaran.
Botnets as a Vehicle for Online Crime – CERT/CC.
Jose Nazario over at Arbonetworks was kind enough to put these references together. As he says, “Read those and you’ll be largely up to date with most IRC bots. Everything since then is largely incremental – crypto, obfuscation, etc. These do not cover P2P bots and HTTP bots, which are becoming hot topics.”