Botnets decentralise after Redmond’s kingpin takedowns

Recent efforts by Microsoft and law enforcement to take down the biggest spamming botnets may have helped pharmaceutical companies but had little effect on overall spam levels.

“After the closure of Rustock in March 2010, the volume of spam sent to the US continued to grow and peaked in April,”  number-crunchers at Kaspersky Labs reported in its latest spam report. 

Spam as a percentage of email in the past quarter grew from 78 percent in April to 84 in June, according to the security software company.

It believed botnet operators were rebuilding infrastructure after the takedowns of several botnet command an control centres, including Rustock in March 2010, and Spamit in October.

M86 Security Labs also rang the alarm bells on Wednesday, claiming it witnessed a sharp surge in malware-laden spam in August.

“From the beginning of August, we have observed a huge surge of malicious spam which far exceeds anything we have seen over the past two years,” said M86’s Rodel Mendrez.

“The majority of the malicious spam comes from the Cutwail botnet,” he said, adding that it contained an attached ZIP file which housed a Trojan that downloads fake antivirus, SpyEye and the Cutwail botnet itself.

Source code for the SpyEye malware -- labelled by some as the “most advanced and dangerous malware kit today” -- was released this week, giving rise to concerns it could become the next Zeus. The code release undermined the reported US$10,000 asking price to start a business based on that malware, and may spawn variants that thwart efforts to prevent its rise.

Spammers responded to the action by law enforcement and Microsoft by increasing the spread of network-building Trojan downloaders last quarter, according to Kaspersky.

Prior to March, the majority of malware sent to the US were financial data-stealing malware, but after this more than half the malware destined for the US was aimed at rebuilding capacity, it reported.

Spammers also increased their reliance on nations with slack cybercrime laws with Indian PCs immediately sending more spam after the takedowns.

The spam game had become more decentralised with no dominant spamming organisation in the world, as well as a diversification of nations that hosted so-called “zombie” machines that are part of a botnet.  

“There are no “botnet free” territories left,” according to Kaspersky. “The zombie machines used to spread spam emails are distributed fairly evenly throughout the world. They are located in South Africa, on distant islands in the middle of the Pacific Ocean and in developed countries.”

The takedowns did however succeed in practically killing off Russian affiliate spam while the nation dropped from its spot as the second highest spammer to the seventh, behind nations in Asia.

Read more articles by Liam Tung

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