NSA whistleblower William Binney warns that the agency collects so much useless information that it can't process it effectively. The Snowden leaks about the MUSCULAR surveillance program (tapping the fiber links connecting up the data-centers used by Internet giants like Google and Yahoo) corroborate Binney's view: in 2013, NSA analysts asked to be allowed to collect less data through MUSCULAR, because the "relatively small intelligence value it contains does not justify the sheer volume of collection."

"What they are doing is making themselves dysfunctional by taking all this data," Mr. Binney said at a privacy conference here.

The agency is drowning in useless data, which harms its ability to conduct legitimate surveillance, claims Mr. Binney, who rose to the civilian equivalent of a general during more than 30 years at the NSA before retiring in 2001. Analysts are swamped with so much information that they can't do their jobs effectively, and the enormous stockpile is an irresistible temptation for misuse…

In a statement through his lawyer, Mr. Snowden says: "When your working process every morning starts with poking around a haystack of seven billion innocent lives, you're going to miss things." He adds: "We're blinding people with data we don't need."