Major technical problems in Iran's nuclear program have forced the temporary shutdown of thousands of centrifuges enriching uranium at Iran's Natanz plant, diplomats told The Associated Press on Monday.

The diplomats said the problems have caused Iranian experts to “briefly power down” the machines they use for enrichment.
The sources said they did not have further details but suspicions focused on the Stuxnet worm, the computer virus which has recently plagued Iran's nuclear program, and is believed by many observers to have been unleashed by the US or Israel. 
Experts said last week that the Stuxnet worm was designed to destroy centrifuges by sending them spinning out of control.
“There have been hints that the program is beset by technical problems,” AP reported. “Even a brief shutdown of the thousands of enriching machines would be the strongest documentation to date that the program – Iran's nuclear cornerstone and a source of national pride – is in trouble.”

Experts said that Stuxnet is believed to be able to send centrifuge speeds up to above-normal levels – up to 1,410 cycles per second – and then suddenly cause the speeds to drop to 2 cycles per second, thus “disrupting their operations and destroying some in the process.”
Another official cited a Western intelligence report suggesting that Stuxnet had “infected the control system of Iran's Bushehr reactor and would be activated once the Russian-built reactor goes on line in a few months.” The virus would then interfere with control of "basic parameters" such as temperature and pressure control as well as neutron flow, he told the news agency. This could result in the meltdown of the reactor.
Iranian enrichment capacity has “stagnated” in recent years, the news agency reported, and hundreds of centrifuges have been taken off line over the past 18 months. A UN official described as close to the International Atomic Energy Agency said a complete stop in Iran's centrifuge operation would be "unprecedented to his knowledge” but would not discuss specifics. AP also spoke to two senior diplomats from IAEA member countries who confirmed the incident at Natanz.
The IAEA is about to issue a confidential update on Iran's nuclear program to its 35-nation board. Three weeks later, talks will resume between Iran and the US, Russia, China, Britain, France and Germany.
Iran has yet to acknowledge that it suspects Israel in the sabotage of its nuclear system's computers. However, if it turns out that Israel has indeed taken control of Iranian centrifuges by means of the Stuxnet virus, this should not come as a surprise to Iranian strongman Mahmoud Ahmadinejad, who has often repeated the anti-Semitic slur that Jews control the world.
"A small handful of Zionists, with a very intricate organization, has taken over the power centers of the world,” the diminutive dictator said in 2008. “According to our estimates, the main cadre of the Zionists consists of  2,000 individuals at most, and they have another 8,000 activists.”