Israel has tested a computer worm aimed at knocking out Iran's nuclear centrifuges, and it seems to have worked, according to a published report.
The New York Times reported on Sunday that the Stuxnet worm shut down a fifth of Iran's nuclear centrifuges in November.
The newspaper said testing of the worm has been taking place for the past two years at a heavily guarded secret nuclear plant at Dimona in the Negev Desert.
There has been no official response from Israel to the story.
Experts interviewed by the newspaper said the Stuxnet worm caused the Iranian centrifuges to spin wildly out of control. They estimated 20 per cent of them have self-destructed.
The worm also reportedly has another feature: to help avoid detection it creates a "situation normal" screen for the computer it has taken over, while it is, in fact, busy destroying the centrifuges.
The New York Times cited unidentified American intelligence experts, including one who said, "To check out the worm, you have to know the machines. The reason the worm has been effective is that the Israelis tried it out."
Iranian centrifuges have been plagued by breakdowns since 2007. Israel recently revised its prediction of the speed of Iran's program. Israel's outgoing intelligence chief Meir Dagan said this month that the expected date for Iran to produce a nuclear weapon has been pushed back to 2015.
Earlier Israeli predictions said Iran was expected to succeed with such production in 1999. Then the date was changed to 2005. Two years ago, Prime Minister Benjamin Netanyahu warned an Iranian nuclear weapons program could be ready by the beginning of 2011.
For its part, Iran is on record as denying it is developing a nuclear weapon and says it only intends to use its nuclear plants for peaceful purposes.