Computers infected with the Conficker worm are being updated with a new variant that sidesteps an industry effort to sever the link between the worm and its hacker controllers, according to researchers at Symantec.
The new version, dubbed Conficker.c, represents the first set of "orders" that researchers have witnessed being sent to infected systems, said Vincent Weafer, vice president of Symantec Corp.'s security response group. The update shows that the hackers want to defend their collection of compromised PCs, Weafer argued.
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Conficker, which is also known as "Downadup," gained notoriety earlier this year when it spread to millions of machines by exploiting a Microsoft vulnerability that the company patched with an emergency update in October 2008. Last month, about 20 technology companies and organizations, including Microsoft, Symantec, VeriSign, and ICANN, the nonprofit group that manages the Internet Domain Name System, joined forces to preemptively register the Internet addresses Conficker's controllers use to maintain their hold on infected machines.
Conficker.c is designed to thwart that work, Weafer acknowledged. While earlier versions of the worm generate a list of 250 possible domains each day that can be used to route instructions from hackers, the new edition cranks out a list of 50,000 URLs.
"Conficker.c makes it even more difficult for us," Weafer said, referring to the work of the so-called Conficker cabal in registering the worm's routing domains. "The sheer volume that would have to be registered would be very challenging," he said, adding that it would "probably not be feasible" to even attempt to register 50,000 domains daily.
The update also beefs up Conficker's defenses against eradication. "It's turning off a variety of security services," Weafer said, as well as tools often used by security companies to dig into malware.
On the bright side, Weafer said that the number of PCs infected with Conficker has peaked, with estimates now in the hundreds of thousands rather than millions. "The number of infected machines is constantly dropping, so we're dealing with a much smaller pool that are potentially getting this update," Weafer said.
And although the cabal's work preemptively registering domains may be coming to a close, Weafer said it was the right move at the time. "The consortium was one mitigation among [others], but before the availability of removal tools, we thought it was the strongest solution," he said. "Now, it will probably become a lesser part."
Other actions that have been taken to stifle Conficker include a $250,000 reward Microsoft has offered for information that leads to the arrest and conviction of the worm's makers.
Users can protect themselves from the worm by installing Microsoft's MS08-067 security update, using strong passwords and disabling Windows' Autoplay and Autorun features.
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