Microsoft has gained a court order shutting down a criminal botnetbelieved to have infected hundreds of thousands of computers around the world.

The so-called ‘Waledac’ botnet is one of the 10 largest inthe US. It is estimated to haveinfected hundreds of thousands of computers around the world and, prior to thetakedown, was believed to have the capacity to send over 1.5 billion spamemails per day.  In a recent analysis, Microsoft found that betweenDecember 3-21, 2009, approximately 651 million spam emails attributable toWaledac were directed to Hotmail accounts alone, including offers and scamsrelated to online pharmacies, imitation goods, jobs, penny stocks and more.

Microsoftinitiated a civil action in the District Court of Eastern Virginia, where thejudge granted leave to shut down 277 Internet domains alleged to command andcontrol the Waledac botnet. The operation, Microsoft said, has “has effectivelyshut down connections to the vast majority of Waledac-infected computers, andour goal is to make that disruption permanent”. 

However, the computerscontrolled by the botnet still carry the infection and affected users need todeal with that problem themselves. A tool to remove Waledac is available here.All Windows users should maintain up-to-date anti-virus programs and firewalls,and apply any security updates issued by Microsoft.