Microsoft has pulled together the resources of researchers, security suppliers and legal experts to shut down the Waledac botnet.
This legal and industry operation against Waledac is the first of its kind, but it won't be the last, said a Microsoft legal representative.
The Waledac botnet is one of the 10 largest networks of compromised computers in the US and a major source of spam and malware, with a top capacity of around 1.5 billion spam e-mails a day.
Microsoft said it was granted permission by a federal judge in a Virginia court to cut off 277 internet domains associated with Waledac.
The operation has shut down connections to the vast majority of Waledac-infected computers, said Tim Cranton, associate general counsel for Microsoft.
"But the operation has not cleaned the infected computers and is not a silver bullet for undoing all the damage we believe Waledac has caused. Although the zombies are now largely out of the bot-herders' control, they are still infected with the original malware," he said.
Cranton said Microsoft has published guidelines on how businesses and consumers can ensure they are not infected by Waledac or other botnets.