On October 14, 2011, a research lab with strong  international connections alerted us to a sample that appeared to be  very similar to Stuxnet. They named the threat "Duqu" [dyü-kyü] because  it creates files with the file name prefix “~DQ”. The research lab  provided us with samples recovered from computer systems located in  Europe, as well as a detailed report with their initial findings,  including analysis comparing the threat to Stuxnet, which we were able  to confirm. Parts of Duqu are nearly identical to Stuxnet, but with a  completely different purpose.
Duqu is essentially the precursor to a future Stuxnet-like attack.  The threat was written by the same authors (or those that have access to  the Stuxnet source code) and appears to have been created since the  last Stuxnet file was recovered. Duqu's purpose is to gather  intelligence data and assets from entities, such as industrial control  system manufacturers, in order to more easily conduct a future attack  against another third party. The attackers are looking for information  such as design documents that could help them mount a future attack on  an industrial control facility.
Duqu does not contain any code related to industrial control systems  and is primarily a remote access Trojan (RAT). The threat does not  self-replicate. Our telemetry shows the threat was highly targeted  toward a limited number of organizations for their specific assets.  However, it’s possible that other attacks are being conducted against  other organizations in a similar manner with currently undetected  variants.
The attackers used Duqu to install another infostealer that could  record keystrokes and gain other system information. The attackers were  searching for assets that could be used in a future attack. In one case,  the attackers did not appear to successfully exfiltrate any sensitive  data, but details are not available in all cases. Two variants were  recovered, and in reviewing our archive of submissions, the first  recording of one of the binaries was on September 1, 2011. However,  based on file compile times, attacks using these variants may have been  conducted as early as December 2010.
One of the variant’s driver files was signed with a valid digital  certificate that expires August 2, 2012. The digital certificate belongs  to a company headquartered in Taipei, Taiwan. The certificate was  revoked on October 14, 2011.
Duqu uses HTTP and HTTPS to communicate with a command-and-control  (C&C) server that at the time of writing is still operational. The  attackers were able to download additional executables through the  C&C server, including an infostealer that can perform actions such  as enumerating the network, recording keystrokes, and gathering system  information. The information is logged to a lightly encrypted and  compressed local file, which then must be exfiltrated out.
The threat uses a custom C&C protocol, primarily downloading or  uploading what appear to be JPG files. However, in addition to  transferring dummy JPG files, additional data for exfiltration is  encrypted and sent, and likewise received. Finally, the threat is  configured to run for 36 days. After 36 days, the threat will  automatically remove itself from the system.
Duqu shares a great deal of code with Stuxnet; however, the payload  is completely different. Instead of a payload designed to sabotage an  industrial control system, the payload has been replaced with general  remote access capabilities. The creators of Duqu had access to the  source code of Stuxnet, not just the Stuxnet binaries. The attackers  intend to use this capability to gather intelligence from a private  entity to aid future attacks on a third party. While suspected, no  similar precursor files have been recovered that predate the Stuxnet  attacks.
You can find additional details in 
our paper here.  The research lab that originally found the sample has allowed us to  share their initial report as an appendix. We expect to make further  updates over the coming days.
Key points:
•    Executables using the Stuxnet source code have been discovered.  They appear to have been developed since the last Stuxnet file was  recovered.
•    The executables are designed to capture information such as keystrokes and system information.
•    Current analysis shows no code related to industrial control systems, exploits, or self-replication.
•    The executables have been found in a limited number of  organizations, including those involved in the manufacturing of  industrial control systems.
•    The exfiltrated data may be used to enable a future Stuxnet-like attack.
Note: At press time we have recovered additional variants  from an additional organization in Europe with a compilation time of  October 17, 2011. These variants have not yet been analyzed. More  information will follow.