Report puts Snowden-like leaks as the No. 2 threat to U.S. security WASHINGTON - Insiders like Edward Snowden who leak secrets about sensitive U.S. intelligence programs pose a potentially greater danger to national security than terrorists, America's spy chiefs warned Wednesday in their annual report to Congress on global security risks. For the first time, the risk of unauthorized disclosures of classified material and state-sponsored theft of data was listed as the second-greatest potential threat to America in a review of global perils prepared by the U.S. intelligence community. The risk followed cyber attacks on crucial infrastructure but was listed ahead of international terrorism. U.S. officials previously have said it will cost billions of dollars to repair or revamp communications surveillance systems in the wake of the disclosures by Snowden, a former contract employee at a National Security Agency listening post in Hawaii who began leaking classified documents to the media in June and who later fled to Russia. Appearing before the Senate Intelligence Committee, James Clapper, the director of national intelligence, said the leaks represent the "most damaging theft of intelligence information in our history." He urged Snowden to return the material, saying he made "the nation less safe and its people less secure." "We've lost critical foreign intelligence collection sources, including some shared with us by valued partners," Clapper said. Terrorists and other adversaries of this country are going to school on U.S. intelligence sources, methods and tradecraft, and the insights that they are gaining are making our job much, much harder. Army Lt. Gen. Michael Flynn, who directs the Defense Intelligence Agency, said the leaks had endangered the lives of intelligence operatives and troops. Matt Olsen, heads of the National Counterterrorism Center, said they had made it tougher to track Al Qaeda and its affiliates. "What we've seen in the last six to eight months is an awareness by these groups ... of our ability to monitor communications and specific instances where they've changed the ways in which they communicate to avoid being surveilled," Olsen said. Investigators believe Snowden copied 1.7 million documents from NSA servers, the largest breach of classified material in U.S. history, although only a fraction have been disclosed so far. Last summer, a military judge sentenced Army Pvt. Chelsea Manning, who was born Bradley Manning, to 35 years in prison for sending 750,000 classified diplomatic cables, military field reports and other material to WikiLeaks. Both Snowden and Manning have been condemned by critics as traitors and hailed by supporters as whistle-blowers who exposed government wrongdoing. Only critics spoke at the hearing. Sen. Susan Collins (R-Maine), said the classified documents Snowden downloaded, if printed out, would form a stack more than three miles high. "It is evident to me that most of the documents stolen by Mr. Snowden have nothing to do with the privacy rights and civil liberties of American citizens or even the NSA collection programs," she said. They pertain to the entire intelligence community and include information about military intelligence, our defense capabilities, the defense industry. Although President Obama has denounced Snowden's actions, he announced plans this month to increase judicial review of the NSA's collection of domestic telephone records and to limit eavesdropping on friendly foreign leaders, two of the programs Snowden exposed. In an interview with German television this week, Snowden said he was seeking to thwart undemocratic mass surveillance by U.S. intelligence. He repeated his claim that an NSA analyst could tap anyone's email account, including that of the U.S. president, an assertion current and former NSA officials hotly deny. The 27-page "Worldwide Threat Assessment of the U.S. Intelligence Community," a report required by Congress, does not mention Snowden by name. But it warns that others may seek to follow his example. "Trusted insiders with the intent to do harm can exploit their access to compromise vast amounts of sensitive and classified information as part of a personal ideology or at the direction of a foreign government," it reads. The unauthorized disclosure of this information to state adversaries, non-state activists or other entities will continue to pose a critical threat. The report repeatedly cites Russia and China as the leading state intelligence threats, both for theft of digital data and for disruption of computer systems, and for more traditional espionage operations aimed at stealing secrets from the U.S. government, the defense industry and elsewhere. "They seek data on advanced weapons systems and proprietary information from U.S. companies and research institutions that deal with energy, finance, the media, defense, and dual-use technology," the report says. The report cites deepening concern about Al Qaeda splinter groups in Syria, Iraq, Yemen and parts of North Africa. But it says a major terrorist attack on America is increasingly unlikely. The threat of complex, sophisticated and large-scale attacks from core Al Qaeda operatives against the U.S. "is significantly degraded," the report says, although it warns that the threat to U.S. facilities overseas has increased. It says Iran has made "concessions on its nuclear program" in order to get relief from international sanctions in a six-month deal with six global powers. "We do not know if Iran will eventually decide to build nuclear weapons," the report says. It adds that Iran has made technical advances that "strengthen our assessment that Iran has the scientific, technical and industrial capacity to eventually produce nuclear weapons. That makes the central issue its political will to do so.