Further research by security firm Symantec uncovered that early versions of the Stuxnet worm may have been in operation as early as 2005, two years earlier than previously thought. Full info at Symantec's blog.
Stuxnet 0.5 is the oldest known Stuxnet variant analyzed to date. This variant stopped compromising computers on July 4, 2009 and stopped communicating with its command-and-control (C&C) servers on January 11 of the same year. The compile timestamps found within most of the code appear unreliable and generally are in the range of 2001.
The main differences between Stuxnet 0.5 and later versions are as follows:
Later versions significantly increased their spreading capability and use of vulnerabilities
Replacement of Flamer platform code with Tilded platform code
Later versions adopted an alternative attack strategy from uranium enrichment valve disruption to centrifuge speed modification