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ASProx botnet dials into Conficker domains

Collusion or collision?

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The zombie network created by the Conficker worm is yet to go "live", but it's displaying curious behaviour that yields potential clues to its origins and purpose.

Variants of the Conficker (Downadup) worm spread by exploiting a vulnerability in the Microsoft Windows server service patched by Redmond in October. It spreads across network shares and via infected USB sticks. The combined approach, allied with social engineering trickery, have made the worm the biggest problem of its kind for years, since the default activation of the Windows firewall put the brakes on the like of Nimda and Sasser.

Compromised Windows PCs are turned into zombie drones, programmed to phone home through a changing (pre-established) list of servers. This behaviour, first analysed by anti-virus firm F-secure, has allowed other security researchers to track the worm's activities.

Jose Nazario, manager of security research, at Arbor Networks, tracked the worm's growth for two weeks leading up to 14 January. "The worm grew explosively in this time period," Nazario reports. The number of unique IPs hitting the sinkhole per day tripled, reaching 12 million by the last day of the study.

Nazario cautions that using neither the figure of unique IPs seen in any one day or the self-reporting value generated by the worm itself to tag infected hosts is necessarily reliable. Nonetheless, the number of infected machines is likely to be "many millions", he concludes.

He also notes that the worm is programmed to avoid infecting Ukrainian hosts, something others have suggested might point to a Ukrainian author for the worm. Russia and Brazil are the two countries individually reporting the greatest number of compromised hosts.

During the time Nazario tracked infected Conficker hosts, he noticed links between the sites used by the worms and websites associated with the ASProx botnet. Some of the anticipated Conficker domains have started to appear on the ASProx botnet over the past week or so.

"The worm has not yet begun to update itself, it seems. Some of the domains were registered and pointed at the ASProx botnet, it appears. Possible hijacking or maybe someone is just running their own numbers for a day. We don’t know. The ASProx botnet did not seem to handle the update checking, however," Nazario writes.

The Asprox botnet has been associated with phishing spam. SQL injection attacks on high-profile websites have become the main mechanism to distribute the malware. The sites used by Conficker were pre-programmed into the malware code so the associations between it and the ASProx botnet are curious - and perhaps a useful subject for further research - but no proof of collusion or co-operation between bot herders and VXer in either group. ®

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