Here's the latest from the Snowden leaks:
The National Security Agency is gathering nearly 5 billion records a day on the whereabouts of cellphones around the world, according to top-secret documents and interviews with U.S. intelligence officials, enabling the agency to track the movements of individuals — and map their relationships — in ways that would have been previously unimaginable.
....The number of Americans whose locations are tracked as part of the NSA’s collection of data overseas is impossible to determine from the Snowden documents alone, and senior intelligence officials declined to offer an estimate. “It’s awkward for us to try to provide any specific numbers,” one intelligence official said in a telephone interview. An NSA spokeswoman who took part in the call cut in to say the agency has no way to calculate such a figure.
An intelligence lawyer, speaking with his agency’s permission, said location data are obtained by methods “tuned to be looking outside the United States,” a formulation he repeated three times. When U.S. cellphone data are collected, he said, the data are not covered by the Fourth Amendment, which protects Americans against unreasonable searches and seizures.
I wonder just how good this "tuning" is?