Director of National Intelligence James Clapper says the danger of a devastating cyberattack is the No. 1 threat facing the U.S. He made the assessment Tuesday on Capitol Hill before the Senate Intelligence Committee hearing on worldwide threats. Susan Walsh/AP hide caption

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Director of National Intelligence James Clapper (center), accompanied by FBI Director Robert Mueller (left) and CIA Director John Brennan, testifies on Capitol Hill on Tuesday. Susan Walsh/AP hide caption

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An Iranian woman shops at a supermarket in the capital, Tehran, on Feb. 22. International sanctions have hurt Iran's economy, but prospects for a breakthrough on Iran's nuclear program are dim as negotiators meet in Kazakhstan. Behrouz Mehri/AFP/Getty Images hide caption

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Some companies, frustrated with intrusions into their networks by cyberattackers, are now trying to turn the tables in the ongoing and complicated cyberwar. iStockphoto.com hide caption

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An analyst looks at code in the malware lab of a cybersecurity defense lab at the Idaho National Laboratory in Idaho Falls, Idaho, Sept. 29, 2011. Jim Urquhart/Reuters/Landov hide caption

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Homeland Security analysts watch for threats to U.S. technological infrastructure at the National Cybersecurity and Communications Integration Center. Jim Watson/AFP/Getty Images hide caption

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John Brennan, the deputy national security adviser for Homeland Security and Counterterrorism, speaks at the White House in January. Brennan is President Obama's choice for CIA director. Carolyn Kaster/AP hide caption

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Egyptian President Anwar Sadat is flanked by senior military officers as he reviews maps of battlefield developments in the 1973 Arab-Israeli War. He's shown at army headquarters in Cairo on Oct. 15, 1973. Egypt and Syria attacked Israel, catching Israel and the CIA off-guard. AP hide caption

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