NSA Chief Claims That Leaks Have Changed Terrorists' Methods of Operation

Says leaks caused "significant, irreversible damage to our nation."

ASPEN, Colo., July 23 (UPI) -- Terrorists have changed their methods of operation because of U.S. secrets leaker Edward Snowden's disclosures, the National Security Agency director said.

"We have concrete proof that they have already -- terrorists groups and others -- are taking action, making changes, and it's going to make our job tougher," Army Gen. Keith Alexander told a moderator from NBC News at the Aspen Security Forum in Colorado.