On 11 November 2008 McColo, a Californian server hosting company, was disconnected from the Internet. This took the controllers for 6 major botnets offline. It has been widely reported that email spam volumes were markedly reduced for some time thereafter. But did disconnecting McColo only get rid of “easy to block” spam?

In a paper presented this week at the Sixth Conference on Email and Antispam (CEAS) I examined email traffic data for for the incoming email to a UK ISP to see what effect the disconnection had.
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