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.

The impact of the takedown—which came at the behest of security researchers—was swift, and noticeable, but not likely to be long lasting. There are indications that Srizbi’s code was intelligent enough that its bots will only be stranded temporarily, utilizing instructions in the code to contact other servers in case the primary controller goes dark.

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