With three 'hops,' U.S. can mine millions of U.S. phone records
It hinges on what's known as "hop" or "chain" analysis. When the NSA identifies a suspect, it can look not just at his phone records, but also the records of everyone he calls, everyone who calls those people and everyone who calls those people.
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"So what has been described as a discrete program, to go after people who would cause us harm, when you look at the reach of this program, it envelopes a substantial number of Americans," said Sen. Dick Durbin of Illinois, the No. 2 Democrat in the Senate.
John Inglis, the NSA's deputy director, conceded the point but said NSA officials "try to be judicious" about conducting hop analysis.
"And so while, theoretically, 40 times 40 times 40 gets you to a large number, that's not typically what takes place," he said. "We have to compare the theory to the practice."
http://www.pressherald.com/news/Government-makes-its-case-to-continue-domestic-surveillance.html?pagenum=full
Oh good - they "try to be judicious". Of course, the public doesn't get to compare the theory to the practice - they have to take the word of 'judicious' people like James Clapper, liar on oath to Congress.