Microsoft has struck a huge blow against one of the Internet's worst sources of spam today. In partnership with security vendors and law enforcement officials, the company successfully executed the internally called "Operation b49" that was just granted a court order to cut off 277 domains associated with the Waledac botnet. The move should effectively sever the connection between the command and control centers of the botnet and most of its thousands of zombie computers around the world.

According to Microsoft, Waledac is one of the 10 largest botnets in the U.S. and a major distributor of spam globally. It is estimated to have infected hundreds of thousands of computers around the world and, prior to this action, was believed to have the capacity to send over 1.5 billion spam emails per day. The majority of the domains ordered cut off are listed as having owners with contact details in China.

Though the link between the botnet and its targets may have been cut, Microsoft notes that there are still many infected computers out there that can be controlled using peer-to-peer techniques. The company is urging its customers to secure and protect their PCs following guidelines posted at