Personally I say Israel was behind this, but the possibility exists the U.S. or even a private individual, possibly a Siemens engineer gone rogue, was behind this... hell for that matter Siemens might have been behind it.
"In the 20th century, this would have been a job for James Bond.
The mission: Infiltrate the highly advanced, securely guarded enemy headquarters where scientists in the clutches of an evil master are secretly building a weapon that can destroy the world. Then render that weapon harmless and escape undetected.
But in the 21st century, Bond doesn't get the call. Instead, the job is handled by a suave and very sophisticated secret computer worm, a jumble of code called Stuxnet, which in the last year has not only crippled Iran's nuclear program but has caused a major rethinking of computer security around the globe." See the rest HERE