The spam-filtering elves that keep inboxes manageable had an easy go of it last week with the shutdown of McColo Corp., a U.S.-based Web hosting firm that analysts estimate hosted command-and-control servers for more than 500,000 bots.

Within hours of the takedown, spam volume decreased by as much as 40 percent, says SecureWorks malware guru Joe Stewart, thanks in large part to the disabling of the "Rustock" and "Srizbi” botnets.

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