A committee of scientific experts has concluded that there is no viable technological alternative to bulk collection of data by the National Security Agency that allows analysts access to communications whose significance only becomes clear years later.

An 85-page report by the National Research Center, commissioned last year in the wake of surveillance revelations by former NSA contractor Edward Snowden, did not take a position on the merits of the intelligence gains from bulk collection of telephone or other records.

But the Obama administration asked the council to look for effective software alternatives to bulk collection. It concluded there weren't any, in cases when, for example, the NSA wants to examine the past communications of new terror suspects.