Israel and the United States jointly tested the Stuxnet computer worm that is believed to have destroyed a fifth of Iran's nuclear enrichment centrifuges, according to an explosive analysis in the New York Times.
The tests were reportedly conducted at Israel's highly guarded Dimona facility, where experts claimed Israel was testing centrifuges almost identical to Iran's enrichment facility in Natanz, sources told the New York Times.
Iran confirmed in November that a computer virus had damaged a "limited number of centrifuges" but claimed that the attack did not affect key systems and that the problem had been quickly resolved.
While neither US or Israeli officials have ever publicly referred to Stuxnet, an outgoing senior Mossad official recently boasted that technological difficulties at Iran's nuclear enrichment facility had knocked back its expected nuclear arms delivery date until 2015.
The New York Times expose cited as evidence Siemen's cooperation in 2008 with the United States government's Idaho National Laboratory - which runs the nation's SCADA security testbed - to identify holes in Siemens' process controller software.
The New York Times also cited WikiLeaks cables that revealed the US successfully prevented 111 Siemens controllers bound for Iran's nuclear facility from reaching its destination in the months before the attack.