Microsoft has succeeded in removing a botnet believed to be capable of sending up to 1.5 billion spam emails per day from the internet.
The company petitioned a US court to allow it to deactivate 277 internet domains believed to be the command and control centres of the suspected network.
Microsoft has meanwhile sued the unknown operators of the network for violating US cybercrime law, and is seeking to track down the defendants through domain registration information.
Microsoft said the Waledac botnet was one of the 10 largest in the US, and had infected hundreds of thousands of computers worldwide.
Analysis suggested the botnet had sent around 651 million spam emails to Hotmail alone during the period between December 3 and December 21, and was capable of sending up to 1.5 billion spams per day, the company added.
“This action has quickly and effectively cut-off traffic to Waledac at the domain registry level, severing the connection between the command and control centres of the botnet and most of its thousands of zombie computers around the world.” Microsoft associate general counsel Tim Cranton said in a blog post.
He added that Microsoft is taking additional measures to downgrade the remaining P2P command and control communication.
The disconnection was conducted in secret to prevent the network's operators from re-establishing connections with the machines.
But Microsoft's actions have angered the US Electronic Privacy Information Center (EPIC). The public interest research group's executive director, Marc Rotenberg, told WSJ that such a strategy could hurt innocent victims.
The WSJ also tracked down the sole US registrant of one the taken-down addresses, Stephen Paluck, who insisted he had done nothing illegal and wanted the domain back.
Security researchers have also questioned the effectiveness of the strategy, according to Computerworld, with analysts from SecureWorks, Spamhaus and Postini all rejecting claims that the Waledac take-down will have any effect on spam levels.