"They succeeded in creating problems for a limited number of our centrifuges with the software they had installed in electronic parts," he told reporters at a media conference, the first time Iran has said a cyberbug affected its centrifuges.
"They did a bad thing. Fortunately our experts discovered that and today they are not able (to do that) anymore," he said.
Iran temporarily halted most of its uranium enrichment work earlier this month, a U.N. nuclear watchdog report said last week, a few days after former IAEA chief Olli Heinonen said the Islamic Republic had had problems with the equipment used in the programme for years and computer virus Stuxnet may be a factor.
In September Iran said that Stuxnet, which experts said may have been created by a state, did not affect Iran's nuclear plant or government systems but did hit computers of staff at the plant and Internet providers.
Stuxnet, a powerful example of the fastest-growing sort of computer bug -- customised malware written specifically to attack a precise target, has attracted publicity through a presumed link to Iran.