Microsoft’s Digital Crimes Unit has disrupted one of the world’s largest purveyors of spam, a complex “botnet” that was capable of sending billions of deceptive emails every day. Operated anonymously under the name Rustock, the botnet sent emails for Microsoft lottery scams as well as fake prescription drugs.

As many as one million computers have been infected by the Rustock botnet, a tool used by cybercriminals to deliver spam emails and engage in other illicit activities.

As part of the investigation, federal authorities seized servers from hosting providers in Seattle and six other cities earlier this week.

Richard Boscovich, a senior attorney in Microsoft’s Digital Crimes Unit, noted in a blog post Thursday that, by working together with federal authorities and other interested parties, they had “successfully severed the IP addresses that controlled the botnet, cutting off communication and disabling it.”

Rustock was a very powerful distributor of spam. In fact, Symantec last year estimated that that it was responsible for 39 percent of the world’s spam emails, according to CNET.

Nick Wingfield at The Wall Street Journal has more details on the operation to wipe out Rustock, noting in his story that the creators of the botnet are not yet known. Some of the John Does — mentioned in a lawsuit filed in U.S. District Court in Seattle — have addresses in Azerbaijan

John Cook is co-founder of GeekWire, a Seattle tech news site. Follow on Twitter: @geekwirenews.

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