Iran recently has mounted a series of disruptive computer attacks against major U.S. banks and other companies in apparent retaliation for Western economic sanctions aimed at halting its nuclear program, according to U.S. intelligence and other officials.

In particular, assaults this week on the Web sites of JPMorgan Chase and Bank of America probably were carried out by Iran, Sen. Joseph I. Lieberman (I-Conn.), chairman of the Homeland Security and Governmental Affairs Committee, said Friday.

“I don’t believe these were just hackers who were skilled enough to cause disruption of the Web sites,” said Lieberman in an interview taped for C-SPAN’s “Newsmakers” program. “I think this was done by Iran and the Quds Force, which has its own developing cyberattack capability.” The Quds Force is a special unit of Iran’s Revolutionary Guard Corps, a branch of the military.

Lieberman said he believed the efforts were in response to “the increasingly strong economic sanctions that the United States and our European allies have put on Iranian financial institutions.”

U.S. officials suspect Iran was behind similar cyberattacks on U.S. and other Western businesses here and in the Middle East, some dating as far back as December. A conservative Web site, the Washington Free Beacon, reported that the intelligence arm of the Joint Chiefs of Staff said in an analysis Sept. 14 that the cyberattacks on financial institutions are part of a larger covert war being carried out by Tehran.

Unlike the cyberattacks attributed to the United States and Israel that disabled Iranian nuclear enrichment equipment, experts said, the Iranian attacks were intended to disrupt commercial Web sites. Online operations at Bank of America and Chase both experienced delays this week.

In a previously undisclosed episode, Iranian cyberforces attempted to disrupt the Web sites of oil companies in the Middle East in August by routing their efforts through major U.S. telecommunications companies, including AT&T and Level 3, according to U.S. intelligence and industry officials. They spoke on the condition that their names not be used because they were not authorized to speak to the press.

The effort did not cause serious disruptions, but it was the largest attempted denial-of-service attack against AT&T “by an order of magnitude,” said an industry official. A distributed denial-of-service, or DDOS, attack is designed to overload a Web site and block access to the server or site.

The U.S. intelligence community is increasingly concerned about Iran’s improving capability to mount attacks. Director of National Intelligence James R. Clapper Jr. told Congress in February that “Iran’s intelligence operations against the United States, including cyber capabilities, have dramatically increased in recent years in depth and complexity.”

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