A bunch of researchers at the University of California Santa Barbara took control of a botnet for ten days, and learned a lot about how botnets work:

The botnet in question is controlled by Torpig (also known as Sinowal), a malware program that aims to gather personal and financial information from Windows users. The researchers gained control of the Torpig botnet by exploiting a weakness in the way the bots try to locate their commands and control servers—the bots would generate a list of domains that they planned to contact next, but not all of those domains were registered yet. The researchers then registered the domains that the bots would resolve, and then set up servers where the bots could connect to find their commands. This method lasted for a full ten days before the botnet’s controllers updated the system and cut the observation short.

During that time, however, UCSB’s researchers were able to gather massive amounts of information on how the botnet functions as well as what kind of information it’s gathering. Almost 300,000 unique login credentials were gathered over the time the researchers controlled the botnet, including 56,000 passwords gathered in a single hour using “simple replacement rules” and a password cracker. They found that 28 percent of victims reused their credentials for accessing 368,501 websites, making it an easy task for scammers to gather further personal information. The researchers noted that they were able to read through hundreds of e-mail, forum, and chat messages gathered by Torpig that “often contain detailed (and private) descriptions of the lives of their authors.”