Ripping the cover off top-secret U.S. surveillance programs pushed foreign terrorists underground and out of intelligence services' reach, a former top intelligence official said Tuesday.
"We've lost collection against some individuals, people that we were concerned about we are no longer collecting their communications," Matt Olsen, who until September led the National Counterterrorism Center, told CNN's Jim Sciutto. "We lost insight into what they were doing."
Olsen said the revelations made public by former NSA contractor Edward Snowden had changed the way terrorists communicate, causing them to fall out of the U.S. government's sight.
"They've changed how they encrypt their communications and adopted more stringent encryption techniques," he said. "They've changed service providers and email addresses and they've, in some cases, just dropped off all together."
Snowden, whose massive leaks on intelligence-gathering programs resulted in espionage charges from the U.S. government, has been living in Russia for the past year. He said during an interview in May that he had no choice other than leaking the highly classified information since he believed the Constitution was being violated.
Government officials, from President Barack Obama down, have uniformly decried the disclosures, though in the years since the information became public there's been open debate about the mass surveillance programs that came to light.
New terror threats have also emerged since Snowden's disclosures, including the ISIS terror group operating in Syria and Iraq, and the al Qaeda offshoot Khorasan that's based in Syria.
Olsen acknowledged terrorists may have suspected their communications were being intercepted before the leaks. But he said Snowden's information confirmed the practice and made it easier for groups to find ways around U.S. surveillance.