Stuxnet has characteristics that demonstrate innovative techniques behind its development. Duqu is an intelligence gathering tool, apparently aiming to prepare the ground for attacks such as StUXnet. DuQu is not equipped with modules for SCADA systems attack, but it is only able to steal information from the host system. DuQ can also be reconfigured remotely to install new malware payloads and to direct attacks at new targets. The ability to compose its structure at different times using modules designed specifically for precise goals, makes this unique and formidable.
Source: https://thehackernews.com/2012/03/face-to-face-with-duqu-malware.html