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Conficker's 6m strong botnet confounds security probes

Cross-industry group baffled by super crypto shield of infamous botnet

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Analysis The unknown crooks behind the infamous Conficker worm may be quietly selling off parts of the huge botnet established by the malware, but virus fighters have no way of knowing because the cryptographic defences of its command and control network have proved uncrackable.

Conficker (aka Downadup) first appeared in November 2008, originally using a recently patched vulnerability in Windows Server Service to infect insecure systems. Later its ability to spread through network shares and to hop over onto PCs from infected USB sticks became its primary spreading mechanism.

Early victims included the Houses of Parliament and the Ministry of Defence in the UK. Conficker's aggressive scanning routines swamped legitimate traffic on compromised networks, creating all sorts of problems in the process.

Interest in the worm peaked around 1 April 2009 when its algorithm changed so that it "phoned home" to a far larger number of pre-programmed domains, sparking fears that new instructions would be applied activating a huge network of zombie computers to send spam or launch denial of service attacks.

In the event, 1 April came and went without anything of note happening, leading some to wrongly label the malware as a damp squib. Although the Conficker botnet remains largely dormant an estimated six million Windows PCs remain infected with the threat.

Wide open backdoor

These Windows boxes remain wide open to further attack not least because Conficker is programmed to turn off Windows update and anti-virus software on compromised machines, according to Rodney Joffe, a director of the Conficker Working Group. The still-active working group is made up of a team of security, domain name, law enforcement and government representatives brought together to fight the Conficker threat.

Early tasks of the group included blocking the registrations of domains that machines infected with early variants of Conficker were programmed to contact for further instructions. Subcommittees of the group focused on issues such as reverse engineering the malware's code, dealing with the sinkhole domains that infected bots were programmed to contact, and community outreach work.

Rodney Joffe, a senior technologist at net infrastructure firm Neustar, dismisses the theory that Conficker was a failed experiment or "research project" by cybercrooks, perhaps one that was too successful to be useful. In particular he's dismissive of the idea that the botnet remains dormant because activating it would provoke unwelcome law enforcement attention.

"Conficker was not a bust. It's still causing enormous problems and damage as a byproduct of infection," Joffe told El Reg.

Around six million systems remain infected with either the A or B variants of Conficker. The C variant, which used a P2P method of distribution, affects a lower number of around 120,000, as illustrated by an infection tracker maintained by the Conficker Working Group here.

Windows PCs infected with the C variant of Conficker were programmed to download Spyware Protect 2009 (a scareware package) and the Waledac botnet client, a strain of malware associated with spamming.

"These are different gangs and suggest the malware authors behind Conficker have a trading relationship with bad guys," Joffe explained.

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