McColo, a major source of spam has been shut down Tuesday . This has lead to spamlevels dropping as much as 75%.
On Tuesday, two major Internet service providers stopped routing traffic for McColo, a hosting provider based in San Jose, Calif., essentially making all sites hosted by the service inaccessible. The action followed investigations by security researchers that found that McColo had become the preferred home of for many botnets’ command and control servers…
So I took a look at the statistics of our anti-spam service, and the cool thing is you can pinpoint the moment when they’ve pulled the plug on them: