New documents declassified by American intelligence officials show the National Security Agency collected up to 56,000 emails of Americans between 2008 and 2011.
The government agency collected the emails, allegedly by accident, despite their senders having no connection with terrorism, Reuters reported.
The disclosures, which come in the form of opinions by the Foreign Intelligence Surveillance Court (FISA), are part of an effort by the Obama administration to calm the controversy after leaks by former NSA contractor Edward Snowden created a global debate about US surveillance tactics.
James Clapper, director of national intelligence, will release three formerly classified documents showing the extent of the alleged errors and, in a sign of the times, post them on his Tumblr blog page.
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Despite Clapper's release of the documents, an intelligence official implied that the director was doing so begrudgingly.
"He's determined that in the current circumstances the harm to national security from release of this information is out weighed by the public interest," said the official, who briefed reporters ahead of the release.
The official said Congress knew there'd be American emails swept up inadvertently in the system during the surveillance programs authorized in 2008.
Politico reported that intelligence officials explained to reporters that the intercepts of American emails were accidental, yet the FISA court did not know about them until three years after they occurred.
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They said the NSA collected thousands of emails, including screengrabs of inboxes, even if the targeted email address may have appeared in only one of the messages.
“For technological reasons, NSA was not capable of breaking those down, and still is not capable, of breaking those down into their individual components,” the official said, according to Politico.
“So if you had a situation where one of those emails may have referenced your targeted email in the subject line, you’d nonetheless collect the whole inbox list. Its like a screenshot, you get whatever is popping up on your screen at the time.”
The emails had apparently been "purged" since then, Reuters said.
The official said the disclosures show "effective self-policing" by the NSA, USA Today reported.