Somewhat technical overview but good stuff. John Levine comments:
Last weekend, Brandon Enright of UC San Diego gave a informal talk at the Toorcon conference in which he reported on his analysis of the Storm botnet. According to his quite informative slides, Storm has evolved quite a lot over the past year, with both upgrades to the underlying engine and a variety of applications, most of which involve sending spam. (If you've gotten pump and dump spam with the message in an MP3 audio file, that's Storm's latest campaign.)
Enright says that although Storm's peer-to-peer control structure makes it harder to map than centrally controlled botnets, its P2P design is relatively simple, and is similar enough to the eDonkey network that he could adapt tools designed for eDonkey to map Storm. While it's never possible to find the exact size of a P2P network since nodes are constantly going on and off line, his statistics suggest that Storm consists of hundreds of thousands of nodes, not millions. While that's a lot, it's in the same range as other botnets. What really sets Storm apart is its operators' skillful social engineering that constantly comes up with new tricks to get people to click on links that infect their Windows PCs.