Last month a pair of US Senators inquired as to how many people within the country had been spied upon by the National Security Agency in the wake of updates to the Foreign Intelligence Surveillance Act (FISA) in 2008. Getting a straightforward answer proved impossible as Senators Ron Wyden and Mark Udall were told that such information would violate the privacy of US persons.

The question was reportedly passed around through the intelligence bureaucracy before landing on the desk of I. Charges McCullough, III, Inspector General of the Office of the Director of National Intelligence, the nominal head of the 16 U.S. spy agencies.

Danger Room acquired a letter dated June 15 from McCullough to both senators where he thanked them for the inquiry and goes on to explain that the request was passed along to NSA Inspector General George Ellard as he would be able to answer the question in a more timely manner.

Ellard concluded that obtaining such an estimate was beyond the capacity of his office and to bring in additional resources needed to get a solid answer would "impede the NSA's mission." NSA leadership agreed that collecting such data would itself violate the privacy of US persons.

"All that Senator Udall and I are asking for is a ballpark estimate of how many Americans have been monitored under this law, and it is disappointing that the Inspectors General cannot provide it," Wyden told Danger Room. "If no one will even estimate how many Americans have had their communications collected under this law then it is all the more important that Congress act to close the 'back door searches' loophole, to keep the government from searching for Americans' phone calls and emails without a warrant."

Wired points out that the FISA Amendment Act allows the NSA to no longer require probable cause to intercept phone calls, text messages or emails so long as one person in the string of communication is "reasonably" believed to be outside of the US.

"If the FISA Amendments Act is not susceptible to oversight in this way, it should be repealed, not renewed," said Steve Aftergood, a secrecy expert at the Federation of American Scientists.