The latest results of a Symnatec study concentrating on the Stuxnet worm revealed that its developers knew what they were doing - once finished, it took only 12 hours to infect the first target.
The study also concluded that the Stuxnet attacks can be dated back to June 2009 - more than a year prior to it being first discovered by security experts - and that its intial targets were five separate organizations that have a presence in Iran and most of which have been attacked at various points through 2009 and 2010.
Israeli general claims Stuxnet attacks as one of his successes
If you want to see a counter-argument see this video. It's long but raises excellent points.