Officials who support the NSA's surveillance program have argued that it's strongly limited and targeted only towards specific people or incidents. But sources have told The Wall Street Journal that the court handling surveillance requests spent the past years broadening the scope of when the NSA can gather data. According to present and former officials familiar with the FISA court, a 2006 decision allowed bulk collection of phone records by defining them as still "relevant" to an investigation, satisfying a legal requirement put in place earlier that year.

The requirement that collected data be "relevant" to an investigation was added when the Patriot Act came up for renewal, and it was meant to create stricter rules. "It wasn't seen that we're pushing the boundaries of surveillance law here," says Timothy Edgar, formerly a privacy lawyer for the National Security Council and the Office of the Director of National Intelligence. "It was the very opposite. You're starting from a huge amount of unilateral surveillance and putting it on a much sounder legal basis."

"It wasn't seen that we're pushing the boundaries of surveillance law here."

Shortly thereafter, though, the Justice Department and NSA started making a case for why relevancy shouldn't limit bulk collection. The offices of Senators Ron Wyden (D-OR) and Mark Udall (D-CO) tell the WSJ that the resulting wide definition of "relevant" information is what they were referring to when they described a "secret interpretation" of US law.

The New York Times revealed similar details last week, saying that according to sources, "the [FISA] court has indicated that while individual pieces of data may not appear 'relevant' to a terrorism investigation, the total picture that the bits of data create may in fact be relevant." The Times' sources also described the FISA court as allowing broad surveillance under the "special needs" provision, which loosens the restrictions on gathering data.

The Times characterized the panel as a "parallel Supreme Court" making security decisions that would have wide implications. "The definition of ‘foreign intelligence' is very broad," said one former official. "An espionage target, a nuclear proliferation target, that all falls within FISA, and the court has signed off on that."