Apparently the stuxnet worm did most harm in the ultra-centrifuges plant at Natanz in Iran.
(New York Times) – In early 2008 the German company Siemens cooperated with one of the United States’ premier national laboratories, in Idaho, to identify the vulnerabilities of computer controllers that the company sells to operate industrial machinery around the world — and that American intelligence agencies have identified as key equipment in Iran’s enrichment facilities.
Siemens says that program was part of routine efforts to secure its products against cyberattacks. Nonetheless, it gave the Idaho National Laboratory — which is part of the Energy Department, responsible for America’s nuclear arms — the chance to identify well-hidden holes in the Siemens systems that were exploited the next year by Stuxnet.
The worm itself now appears to have included two major components. One was designed to send Iran’s nuclear centrifuges spinning wildly out of control. Another seems right out of the movies: The computer program also secretly recorded what normal operations at the nuclear plant looked like, then played those readings back to plant operators, like a pre-recorded security tape in a bank heist, so that it would appear that everything was operating normally while the centrifuges were actually tearing themselves apart.
Siemens PLC systems were present on the Deepwater Horizon. Not likely stuxnet worm involved in sinking of the oil rig.
Buried in the code, experts found a concealed reference to the word “MYRTUS”, believed to refer to the Myrtle tree, or Hadassah in Hebrew. This was apparently the birth name of the former Jewish queen of Persia, Queen Esther whom the Bible describes as having persuaded her husband to launch a pre-emptive strike on Persian forces, before his own forces were attacked. The virus is most likely to have been introduced into the Iranian systems by a Russian technician, unknowingly, by means of a USB memory stick.