Researchers are fairly confident that whoever wrote the Duqu malware also was involved in some way in developing the Stuxnet worm. They re confident that they have not yet identified all of the individual components of Duqu, meaning that there are potentially some other capabilities that haven t been documented yet. Despite its huge public profile, Duqu is not a widespread piece of malware, experts say. The malware is being used in highly specific attacks against carefully chosen targets, and in virtually every known case, the attackers have used different encryption methods and different files.
Source: https://threatpost.com/researchers-convinced-duqu-written-same-group-stuxnet-111611/75902/