The Stuxnet computer worm helped slow Iran's nuclear programme but failed to stop the Islamic Republic's continued stockpiling of enriched uranium, a US-based think-tank said in a report.
Stuxnet is believed to have destroyed in late 2009 or early 2010 about 1,000 centrifuges -- machines used to refine uranium -- out of 9,000 deployed at Iran's Natanz enrichment plant, the Institute for Science and International Security (ISIS) said.
"The effect of this attack was significant," ISIS experts David Albright, Paul Brannan and Christina Walrond wrote in the analysis posted on the institute's website on Feb. 15.
"It rattled the Iranians, who were unlikely to know what caused the breakage, delayed the expected expansion of the plant and further consumed a limited supply of centrifuges to replace those destroyed."
But Iran took steps that likely reduced further damage by Stuxnet and shut down many centrifuges, finely calibrated cylindrical devices that spin at supersonic speed to increase the fissile element in uranium, ISIS said.
"While it has delayed the Iranian centrifuge programme at the Natanz plant in 2010 and contributed to slowing its expansion, it did not stop it or even delay the continued buildup of LEU (low-enriched uranium)," the report said.
Any setbacks in Iran's enrichment campaign could buy more time for efforts to find a diplomatic solution to its stand-off with world powers, even though talks in Geneva in December and Istanbul last month failed to bridge the gap.
Enriched uranium can be used to fuel nuclear power plants, which is Iran's stated aim, or provide material for bombs if processed much further. Western powers accuse Iran of seeking to develop nuclear weapons capability.
Security experts say Stuxnet, which has been described as a first-of-its-kind guided cyber missile, may have been an attempt by Iran's foes to sabotage its nuclear programme, possibly carried out by Israel or the United States.
Iran's atomic activities have also been suffering from design-related technical woes and increasingly tough sanctions which make it more difficult for Tehran to acquire the equipment and other material it needs for its enrichment work.
Despite such problems, diplomats and experts say Iran has resumed steady enrichment after a brief halt late last year and that it has now has amassed enough enriched uranium for one or two bombs if refined much more.
ISIS said cyber attacks such as Stuxnet were likely to continue in the absence of a diplomatic settlement.
"They provide an alternative to military strikes against Iran's known nuclear sites, a tactic that most see as likely to be ineffectual or counterproductive," the report said.
Israel and the United States have not ruled out military action if diplomacy fails to resolve the dispute.
The risk of the row escalating into a military conflict appeared to recede last month when the departing head of Israeli espionage agency Mossad said Iran, the Jewish state's arch-foe, might not have a nuclear weapon before 2015.
But that was later contradicted by the new head of Israel's military intelligence, who said sanctions had not held up Iran's nuclear programme and it could produce bombs within two years.