The Iranians said the attack was timed to follow the failure of talks in Moscow to convince Tehran to abandon its nuclear program, which the Americans and their allies suspect masks a drive to develop nuclear weapons. Iran denies that.
There has been no indication from U.S., British or Israeli authorities that they had undertaken such an attack.
But Iran has been the target of at least two, and possibly more, cyberattacks by the United States and Israel since 2009.
The development of increasingly powerful cyber weapons points to an intention to continue efforts to sabotage Iran's nuclear project, which the Israeli leadership under hawkish Prime Minister Binyamin Netanyahu views as an existential threat to the Jewish state.
Iranian Intelligence Minister Heydar Moslehi was quoted as saying on state television Thursday, "They still seek to carry out the plan but we've taken necessary measures."
He gave no details about what those measures might be. Indeed, there was no independent verification that any such attack had taken place.
It may be that Tehran was simply seeking to deflect criticism of its refusal to accede to the demands of the P5+1 powers -- the five permanent members of the U.N. Security Council plus Germany.
But a major cyberattack on Iran's nuclear infrastructure, particularly its uranium-enrichment program, a key process in developing weapon-grade nuclear material, now would seem appropriate.
The talks in Moscow on Monday and Tuesday, the third round of negotiations since April, broke down with no progress. Western diplomats said the Iranians refused to make any commitment toward the key demand that it limit uranium enrichment to 20 percent, below military requirements.
They refused to discuss their new enrichment plant at Fordow, near the holy city of Qom south of Tehran. This facility, opened last year, is built into a mountain and supposedly safe from air attacks, unlike the enrichment center at Natanz, in central Iran.
If Fordow is invulnerable from the air, subjecting the enrichment program to cyberattack seems a logical alternative and much less risky in terms of casualties.
In this regard, the enrichment process has been the primary target of the so-called Stuxnet computer virus used in 2009 and 2010. Those attacks sabotaged the enrichment process but the Iranians were able to resume it later.
Computer experts say Stuxnet was created by the Americans and Israelis.
The Washington Post reported June 1 U.S. President Barack Obama secretly ordered cyberattacks on Iran's nuclear facilities within weeks of taking office.
Several weeks ago, Iran's nuclear program came under cyberattack again, this time from an even more virulent cyber weapon identified as W32.Flame. This one not only penetrates a system but is able to steal vast amounts of sensitive data and even turn on cameras and PC microphones to obtain additional data or change settings on computer systems.
The Symantec security firm reported June 8 that the creators of the Flame malware, considered the most dangerous virus so far developed, sent a "suicide command" that removes it from some infected computers.
In June 4, a week after Flame was uncovered, the Israeli military admitted for the first time it uses cyberspace for offensive purposes to gather intelligence, attack Israel's enemies and conduct secret operations.
The day Flame was discovered, Israeli Deputy Prime Minister Moshe Yaalon dropped broad hints that the Jewish state's military and intelligence community was behind the cyber attack on Iran's nuclear program.
"These achievements of ours open all kinds of possibilities for us," he commented.
The main unit involved in Israel's cyber operation is Unit 8200, arguably the most secret organization in the Israel military. It's the equivalent of the United States' National Security Agency or Britain's General Communications Headquarters.
Unit 8200 is responsible for signals intelligence, electronic eavesdropping, code decryption and all offensive cyber operations.
The defense of Israeli networks is the responsibility of another organization, the C4I Directorate -- for command and control, communications and computers plus intelligence.
The Iranians haven't been idle and are no doubt striving to develop countermeasures or offensive malware to retaliate.
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