Mailbox-level reduction may depend on spam detection methods.
When the rogue provider
McColo
was taken offline in November 2008, depriving many botnets of their command and control systems, global spam levels were reported to have dropped by as much as 60%. However, new research shows that this drop was not experienced as such by all recipients and that some anti-spam methods became less effective after the shutdown.
Richard Clayton of the University of Cambridge, UK, studied the incoming mail stream of a medium sized ISP in the weeks before and after
McColo
was taken down and presented the results in a paper at last week’s
CEAS
conference. As expected, he found a significant drop in the total amount of spam received in the weeks following the shutdown.
However, most of this drop was measured at the first steps of the pipeline of spam detection methods, where email sent from blacklisted IP addresses or to non-existent email addresses is discarded. The reduction of spam seen at the last step in the pipeline, where the content of the email was scanned, was a lot smaller. Users relying on a spam filtering system that depends largely on the use of blacklists will thus not have seen the amount of spam in their inboxes greatly reduced.
More at the University’s
Light Blue Touchpaper
blog
here
, while a PDF of the paper can be downloaded
here
.
Posted on 21 July 2009 by
Virus Bulletin
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