It was frustrating news for computer users when Symantec researchers on Friday last week reported that they have found that Conficker creators have released a new variant of the Conficker worm, which infected millions of PCs worldwide last year.

The vice president of security response group of Symantec Corp., Vincent Weafer reported that the new variant of the Conficker worm is the updated version of Conficker worm. The new variant of the Conficker has been named as "Conficker. c," which indicates that the hackers intend to defend their collection of compromised PCs.

According to Symantec researchers, Conficker. c has been unleashed to hinder the effort of the technology companies & organizations that joined their powers to combat Conficker worm and its creators.

Conficker, also known as "Downadup," infected millions of PCs worldwide by exploiting a Microsoft vulnerability, last year. Last month, about twenty tech firms and organizations including Microsoft, Symantec, VeriSign Inc. and ICANN, the nonprofit group that manages the Internet Domain Name System, got together to record the Internet addresses the controllers of Conficker use to maintain their hold on infected machines.

Symantec researchers reported that 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.

Commenting on the work of the so-called "Conficker cabal" in registering the worm's routing domains, Weafer said, "Conficker. c makes it even more difficult for us. The sheer volume that would have to be registered would be very challenging." He added that it would "probably not be feasible" to even attempt to register 50,000 domains daily.

Symantec researchers accounted that the updated Conficker. c identifies antivirus software or security analysis tools running on a infected PC, and attempts to shut down those programs. Thus, Conficker. c strengthens defenses against eradication. Weafer said, "It's turning off a variety of security services and tools often used by security companies to dig into malware."

Weafer said that the bright side is that the number of PCs presently infected with Conficker is in the hundreds of thousands rather than millions. Weafer said, "The number of infected machines is constantly dropping, so we're dealing with a much smaller pool that are potentially getting this update."

Symantec researchers notified that the users install Microsoft's MS08-067 security update, using strong passwords and disabling Windows' Autoplay and Autorun features to protect themselves from 'Conficker. c'.