Largest botnet as of 2006: 1.5 M machines

From Gregg Keizer’s “Dutch Botnet Bigger Than Expected” (InformationWeek: 21 October 2005):

Dutch prosecutors who last month arrested a trio of young men for creating a large botnet allegedly used to extort a U.S. company, steal identities, and distribute spyware now say they bagged bigger prey: a botnet of 1.5 million machines.

According to Wim de Bruin, a spokesman for the Public Prosecution Service (Openbaar Ministerie, or OM), when investigators at GOVCERT.NL, the Netherlands’ Computer Emergency Response Team, and several Internet service providers began dismantling the botnet, they discovered it consisted of about 1.5 million compromised computers, 15 times the 100,000 PCs first thought.

The three suspects, ages 19, 22, and 27, were arrested Oct. 6 …

The trio supposedly used the Toxbot Trojan horse to infect the vast number of machines, easily the largest controlled by arrested attackers.