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The National Security Agency has overstepped its authority on thousands of occasions each year since being granted sweeping new powers in 2008, according to an internal audit and other documents leaked by Edward Snowden. Most of the illegal activity involved surveillance of Americans, or of foreign nationals on U.S. soil, with some incidents apparently stemming from human error. "We're a human-run agency operating in a complex environment ... so at times we find ourselves on the wrong side of the line," a senior NSA official told The Washington Post.

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