wiredmikey writes "The Rustock Botnet was sending as many as 13.82 billion spam emails each day before being taken down early this month by an effort headed by Microsoft in cooperation with authorities and the legal system. According to Symantec's March 2011 MessageLabs Intelligence Report, the Rustock botnet had been responsible for an average of 28.5% of global spam sent from all botnets in March. Following the takedown, when the Rustock botnet was no longer cranking out spam by the billions, global spam volumes fell by one-third. For reference, toward the end of 2010, Rustock had been responsible for as much as 47.5% of all spam, sending approximately 44.1 billion e-mails per day, according to MessageLabs stats. Since then, Bagle, a botnet that wasn't even on MessageLabs' top ten spam-sending botnets at the end of 2010, has taken over from Rustock as the most active spam-sending botnet this year."