From Jacqui Cheng’s “Report: botnets sent over 80% of all June spam” (Ars Technica: 29 June 2009):
A new report (PDF) from Symantec’s MessageLabs says that more than 80 percent of all spam sent today comes from botnets, despite several recent shut-downs.
According to MessageLabs’ June report, spam accounted for 90.4 percent of all e-mail sent in the month of June—this was roughly unchanged since May. Botnets, however, sent about 83.2 percent of that spam, with the largest spam-wielding botnet being Cutwail. Cutwail is described as “one of the largest and most active botnets” and has doubled its size and output per bot since March of this year. As a result, it is now responsible for 45 percent of all spam, with others like Mega-D, Xarvester, Donbot, Grum, and Rustock making up much of the difference