According to a Virginia court order, Microsoftgot control over 276 domains that previously constituted the core of a botnet known as Waledac .
Waledac is a botnet that used computers infected with a special trojan to send spam. The peak of the botnet's work came in 2009, when this network sent up to 1.5 billion spam messages every day. Microsoft notes that the Hotmail email service recorded up to 650 million spam mailings. ')
After obtaining control over the botnet and its neutralization, Microsoft was able to record the circulation of infected computers. So for 7 days, 58,000 computers tried to contact the botnet, which made more than 14.6 million attempts to connect to the rendered harmless domains.
Microsoft is working with providers that can inform their customers about the infection. So provider Cox Communications has contacted hundreds of its clients to report that their computers are infected. To remove the Trojan from the system and prevent infection, simply install the free Microsoft Security Essentials antivirus.
Details of the destruction of a botnet can be found in this article on the Microsoft website.