U.S. Marshals seized command and control servers that ran the Rustock botnet. Rustock was a key cog in the global spam and malware economic machine. It was responsible for sending billions of junk emails a day that pushed a laundry list of garbage products. Estimates put the amount of spam from Rustock at roughly half of the worldwide junk email volume. This is the second major botnet disruption that Microsoft has initiated, coming roughly a year after the company went after the Waledac network with similar tactics.
Source: https://threatpost.com/microsoft-fireeye-take-down-notorious-rustock-botnet-031811/75043/