The tests were carried out in Israel's nuclear facility in Dimona on the centrifuges that are believed to be identical to those at the Iranian nuclear site in Natanz.

"Dimona tested the effectiveness of the Stuxnet computer worm, a destructive program that appears to have wiped out roughly a fifth of Iran's nuclear centrifuges and helped delay, though not destroy, Tehran's ability to make its first nuclear arms," the report said.

"To check out the worm, you have to know the machines," a U.S. expert told the newspaper. "The reason the worm has been effective is that the Israelis tried it out."

In September, Iran announced that the Stuxnet virus attacked the computers of employees at the Bushehr nuclear power plant but it did not hamper the work.

Iranian President Mahmoud Ahmadinejad admitted in late November that the "enemies" of Iran created limited problems for the country's uranium enrichment centrifuges.

Western powers suspect Iran of building nuclear weapons under the guise of a peaceful nuclear program, an accusation Tehran strongly denies.