Yesterday Microsoft announced a successful, collaborative effort to deactivate a major botnet, called win32/Waledac. 

Botnets are networks of compromised personal and business computers controlled remotely and secretly by one or more cybercriminals. Botnets send massive amounts of unsolicited e-mail messages and they are lucrative -- their controllers get rich by scamming people into sending money for fraudulent purposes. 

Since Microsoft and others joined forces to deactivate Waledac, up to 90 percent of previously controlled computers have been released from the botnet.

Prior to the botnets deactivation, Microsoft estimated that Waledac infected hundreds of thousands of computers around the world and had the capacity to send over 1.5 billion spam e-mail messages per day. Microsoft also found that between December 3 and December 21, 2009,Waledac was responsible for approximately 651 million spam e-mail messages directed to Hotmail accounts alone, including offers and scams related to online pharmacies, imitation goods, jobs, penny stocks, and more.

For more information about the Microsoft effort to take down botnets and help reduce spam and fraud, see Deactivating botnets to create a safer, more trusted Internet.