(CBS News) The New York Times reported Monday that a leak of classified information to reporters appears to have cost the United States a key source of information about al Qaeda.
The leak concerned how the U.S. learned of a recent plot to attack U.S. embassies.
Monday, the attorney general said leaks of that nature do serious damage.
Nineteen U.S. diplomatic offices were quickly closed across the Arab world in early August after intelligence analysts heard al Qaeda boss Ayman al-Zawahiri and Yemen commander Nasser al Wuhayshi planning attacks.
But when newspapers, including The New York Times, revealed those intercepts, the al Qaeda communication channel went silent. Attorney General Eric Holder said that's now making it harder to track terrorists.
"These leaks are serious," Holder said. "They are consequential. They have negative impacts. They cause changes in behavior by the people who we are struggling against."
Sources say the leaks of classified files by former National Security Agency contractor Edward Snowden have also caused irreparable harm.
Snowden disclosed NSA secrets showing the government scoops up phone and internet records. The files were among the 20,000 classified documents Snowden took with him to Hong Kong and Russia.
"It's a tremendous boon to our foreign opponents," said Jim Lewis, who has advised the Pentagon and the White House on cyber defense.
Lewis believes Snowden's files are almost certainly in the hands of Chinese and Russian intelligence.
"The ability of a foreign intelligence analyst to now sit down and look at this treasure trove of material on NSA and how it operates and its programs and its budget, on everything, will give them immense insights," he said.
Is this the kind of information Chinese and Russian intelligence would be happy to pay for?
"They would be happy to pay for, steal, do whatever they could to get it," Lewis said.
U.S. intelligence now has to rebuild, he said.
Now al Qaeda has not gone completely silent and that's good news. Analysts say it is a must for any terror group, including al Qaeda, to communicate and as long as they are talking in some form the United States has some ability to keep track of them.
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