Microsoft had filed a lawsuit in civil court against "John Does … controlling a computer botnet and thereby injuring Microsoft and its customers." The lawsuit was unsealed on Thursday by a federal judge, at Microsoft's request.
Richard Boscovich, senior attorney in the Microsoft Digital Crimes Unit (DCU), said in a blog post on Thursday that "the Rustock botnet was officially taken offline yesterday, after a months-long investigation by DCU and our partners, successful pleading before the U.S. District Court for the Western District of Washington, and a coordinated seizure of command and control servers in multiple hosting locations escorted by the U.S. Marshals Service."
The operation to bust Rustock, which infected an estimated one million computers, built on knowledge Microsoft gained when it took down Waledac last year. "Like the Waledac takedown, this action relied on legal and technical measures to sever the connection between the command and control structure of the botnet and the malware-infected computers operating under its control," said Boscovich.
Security firm FireEye and the University of Washington filed declarations of support for Microsoft's suit, as did drug-maker Pfizer, since the bulk of Rustock's spam purported to sell drugs such as the company's Viagra.
In Pfizer's declaration, Patrick Ford, senior director in the Americas region for Pfizer Global Security, said that investigations conducted by Pfizer in the U.S. and France procured drugs advertised as Viagra via spam emails. In both cases, the spam emails resolved to the same Web site: doctorroe.com. The procured samples, which were tested at Pfizer labs, turned out to be either counterfeit versions from China and Hong Kong, or unapproved, generic versions from India.
Rustock first went dark on Wednesday, a development first reported by security writer Brian Krebs .
While many botnets serve as conduits for enormous quantities of email spam, of late Rustock was the most prolific, at times generating 2,000 messages per second. "For the last year or so, Rustock has been the dominant source of spam in the world, by the end of 2010, accounting for as much as 47.5% of all spam," said Paul Wood, MessageLabs Intelligence senior analyst at Symantec, in a blog post. "At its peak it was responsible for more than half of all global spam."
But unfortunately, according to multiple security firms, Rustock's takedown didn't appear to impact global spam levels, which have remained steady, despite the takedown.
"The takedown of Rustock hasn't had much noticeable effect on the overall amount of spam tracked by MessageLabs Intelligence," said Wood on Thursday. "So far in fact, traffic looks normal."