Of all the people spied on by the US government, 90% are said to have been ordinary internet users rather than foreign surveillance targets.
The claim was published in the Washington Post newspaper which said that innocent people were "caught in a net the National Security Agency had cast for somebody else".
The information came from former NSA contractor Edward Snowden, and the newspaper said it reviewed some 160,000 emails and instant-messages and 7,900 documents from some 11,000 online accounts, gathered by the NSA between 2009 and 2012.
The Post said that its four-month investigation showed that nine out of 10 of the account holders - including many Americans - were not the intended surveillance targets.
Much of the information has, the paper says, a "startlingly intimate, even voyeuristic quality" telling stories of "love and heartbreak, illicit sexual liaisons, mental-health crises, political and religious conversions, financial anxieties and disappointed hopes".
But the intercepted material also contained "discoveries of considerable intelligence value", such as "fresh revelations about a secret overseas nuclear project, double-dealing by an ostensible ally, a military calamity that befell an unfriendly power, and the identities of aggressive intruders into US computer networks", it said.
So, while private lives have been secretly monitored, intelligence information has been gathered. This undoubtedly will, or at least should, pose a moral dilemma for the US authorities.
After his spectacular leaks over NSA spying, Mr Snowden fled the US in May last year and now has temporary asylum in Russia.
Comments
Now ... when will the Portuguese Police identify their own Portuguese jihadists in their homeland ?