America's spy agencies are so focused on "mass surveillance" that they have missed clues about terrorist incidents, such as last year's Boston Marathon bombing and an attempted attack on a jetliner on Christmas Day in 2009, former intelligence contractor Edward Snowden said.
In an hour-long video discussion hosted by the South by Southwest music, film and technology conference in Austin, Texas, Snowden - who is living in asylum in an undisclosed location in Russia - said the National Security Agency's efforts to collect information in bulk had backfired.
"We've actually had a tremendous intelligence failure because ... we're monitoring everybody's communications instead of suspects' communications" - a situation, he said, that had "caused us to miss" intelligence.
Snowden, who faces espionage charges for disclosing top-secret intelligence documents to journalists, has prompted a global debate about surveillance and forced the US government to be more transparent about once-classified programmes.
His actions have drawn harsh criticism from senior US officials, who contend that the leaks have put national security at risk, as well as approval from technologists and privacy advocates, who say the leaks have forced tech companies to make their systems more secure.
Watch: NSA leaks fueled needed debate, Snowden tells SXSW
"Let me be clear about one thing," said American Civil Liberties Union principal technologist Christopher Soghoian, one of two ACLU representatives who took part in the discussion with Snowden: "His disclosures have improved internet security."
Snowden, who was using a Google video-conferencing programme that ran through seven proxy servers to mask his location, used much of his talk to urge companies and technologists to develop and adopt easier-to-use encryption.
"It has to happen seamlessly," he said.
Encryption, he said, enabled him to protect the information he took from the NSA, where he worked until last spring. US officials "still have no idea of what documents were provided to journalists, what they have and don't have, because encryption works", he said.
He also said that neither the Chinese nor the Russian governments possessed any of the information he took. Snowden spent a short time in Hong Kong before arriving in Moscow last year.
The intelligence failures Snowden alleged are not clear-cut. The Christmas 2009 bomb attempt involved a failure to connect and understand the information agencies possessed. In the Boston case, the FBI followed up on a tip from Russian authorities about a suspect but found insufficient grounds to open a criminal investigation.
General Keith Alexander, the NSA director, has vigorously defended the agency's activities. "The press has articulated them as the villains, when what they're doing is protecting this country and doing what we have asked them to do," he told Congress last month. "And if they've made a mistake, we find out, oh, they reported that three years ago to the courts, to Congress and to the administration."
The documents shared with journalists by Snowden have resulted in reports about the NSA's collection activities overseas and in the United States.