The National Security Letter (NSL) is a potent surveillance tool that allows the government to acquire a wide swath of private information—all without a warrant. Federal investigators issue tens of thousands of them each year to banks, ISPs, car dealers, insurance companies, doctors, and you name it. The letters don't need a judge's signature and come with a gag to the recipient, forbidding the disclosure of the NSL to the public or the target.

For the first time, as part of a First Amendment lawsuit, a federal judge ordered the release of what the FBI was seeking from a small ISP as part of an NSL. Among other things, the FBI was demanding a target's complete Web browsing history, IP addresses of everyone a person has corresponded with, and records of all online purchases, according to a court document unveiled Monday. All that's required is an agent's signature denoting that the information is relevant to an investigation.

"The FBI has interpreted its NSL authority to encompass the websites we read, the Web searches we conduct, the people we contact, and the places we go. This kind of data reveals the most intimate details of our lives, including our political activities, religious affiliations, private relationships, and even our private thoughts and beliefs," said Nicholas Merrill, who was president of Calyx Internet Access in New York when he received the NSL targeting one of his customers in 2004.

The FBI subsequently dropped demands for the information on one of Merrill's customers, but he fought the gag order in what turned out to be an 11-year legal odyssey just to expose what the FBI was seeking. He declined to reveal the FBI's target.

The NSL got a major boost in the wake of the 2001 terror attacks, as it became part of the USA Patriot Act. Between 2003 and 2005, the FBI issued 143,074 NSLs according to a Justice Department inspector general report.

Jameel Jaffer, the American Civil Liberties Union deputy legal director, said that "the FBI has imposed effectively permanent gag orders on tens of thousands of NSL recipients... This kind of secrecy prevents the public from learning how the government’s surveillance authorities are used, distorts public debate, shields policymakers from accountability for their decisions, and insulates surveillance powers from judicial review."

Merrill's lawsuit took six years before he was able to say he received an NSL targeting one of his customers. Litigation continued until Monday, when Merrill was finally allowed to disclose what the FBI was demanding.

The government fought disclosure of an attachment detailing what the FBI was seeking, claiming its exposure would harm national security. A judge disagreed.

"If the Court were to find instead that the Government has met its burden of showing a good reason for non-disclosure here, could Merrill ever overcome such a showing?" US District Judge Victor Marrero ruled (PDF). "Under the Government's reasoning, the Court sees only two such hypothetical circumstances in which Merrill could prevail: a world in which no threat of terrorism exists, or a world in which the FBI, acting on its own accord and its own time, decides to disclose the contents of the Attachment."

In January, President Barack Obama directed the Justice Department to "amend" gag orders so that they are not permanent. According to the Director of National Intelligence: