Study: Uptick in spam-sending zombie PCs in September

Symantec attributes the growth to an increase in e-mail with sensationalistic news headlines that include links to downloadable malware.

Compromised computers that send spam as part of their regular botnet activity increased dramatically in September, according to a Symantec study (PDF) released Monday.

The Symantec report follows a study from MessageLabs also illustrating the increased use of automated spam relays.

After seeing a 37 percent drop in botnet-related spam for August, Symantec reported a 101 percent increase in September. The growth appears to be focused in Europe, the Middle East, and Asia, with South Korea experiencing the largest increase at 4,236 percent. It was followed by Kazakhstan (761 percent), Romania (607 percent), Saudi Arabia (555 percent), and Vietnam (540 percent).

Compromised PCs sending spam had been part of the background noise until recently, when their usage surged in September. Symantec

In looking for a reason behind the one-month increase, Symantec speculated it had something to do with the increase in e-mail with sensationalistic news headlines that included links to downloadable malware. These include malicious spam campaigns emulating e-mail from CNN and MSNBC.

Turkey topped the list of countries hosting spam-sending compromised PCs, responsible for 12 percent of such traffic, according to Symantec. It was followed by Brazil (9 percent), Russia (8 percent), the U.S. (6 percent), India (6 percent), China (6 percent), Germany (5 percent), Argentina (4 percent), Poland (4 percent), and Thailand (3 percent).

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