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Duqu' used in targeted attacks to steal specific information.

Researchers at both Symantec and McAfee have discovered a new Remote Access Trojan (RAT) with strong links to Stuxnet being used in some highly targeted attacks.

The trojan, which has been named 'Duqu' after the files with prefix ~DQ it creates, shares source code with Stuxnet - which indicates that its authors had access to this code and may indeed have been the authors of Stuxnet.

Unlike Stuxnet, which targeted industrial control systems, Duqu appears to be designed solely for stealing information: it contains a keylogger and monitors system activity.

Because of this, and because the trojan is highly targeted at a small number of organisations (among which, according to Symantec, are manufacturers of industrial control systems), it is speculated that it is being used as a precursor of a Stuxnet-like attack: the information obtained by Duqu could be used to attack control systems. It has not been revealed what kind of systems are being targeted, or in which country they reside.

One of Duqu's driver files is digitally signed by a certificate belonging to a Taiwanese company; Stuxnet was signed by certificates belonging to two Taiwanese companies. Symantec researchers believe that this certificate is stolen, rather than falsely generated. It has since been revoked.

McAfee researchers believe that Certificate Authorities (CAs) themselves are among the targets of the attack - in particular those CAs residing in or around the Middle East. The importance of such CAs was seen earlier this year when attackers managed to have rogue certificates signed by Comodo andDigiNotar.

More details at Symantec here and at McAfee here. To recap on what Stuxnet was all about, these FAQs atF-Secure may be helpful.