Microsoft claims it has helped disable a “botnet” network purportedly responsible for sending billions of spam e-mails daily – at its peak, nearly half the spam afflicting computers worldwide. Microsoft worked with law enforcement officials to disable the computers responsible for controlling the network.

[ad#Google Adsense 300×250 in story]The network, known as Rustock, is known for distributing “fake Microsoft lottery scams and offers for fake – and potentially dangerous – prescription drugs,” according to Richard Boscovich, senior attorney with Microsoft’s Digital Crimes Unit (DCU).

Microsoft also worked with Pfizer, the pharmaceutical company, network security provider FireEye and University of Washington security experts to identify to the courts how exactly the Rustock spam presented a public danger. According to court documents submitted by Pfizer, for example, Rustock spam offered unapproved knockoff drugs based on Pfizer products.

Rustock malware infects Windows-based PCs and turns them into bots – systems able to be remote-controlled by “bot-herder” computers. Bot-herders then use the remote systems to send large volumes of spam e-mail to unsuspecting recipients.

Individual PCs infected with Rustock malware remain untreated, but Microsoft’s actions have rendered those machines inoperative … at least for the moment.