A national security letter cannot be used to authorize eavesdropping or to read the contents of e-mail. But it does permit investigators to trace revealing paths through the private affairs of a modern digital citizen. The records it yields describe where a person makes and spends money, with whom he lives and lived before, how much he gambles, what he buys online, what he pawns and borrows, where he travels, how he invests, what he searches for and reads on the Web, and who telephones or e-mails him at home and at work.

What exactly is a national security letter?

Issued by FBI field supervisors, national security letters do not need the imprimatur of a prosecutor, grand jury or judge. They receive no review after the fact by the Justice Department or Congress. The executive branch maintains only statistics, which are incomplete and confined to classified reports. The Bush administration defeated legislation and a lawsuit to require a public accounting, and has offered no example in which the use of a national security letter helped disrupt a terrorist plot.

You can view a sample letter here.(pdf)

Before the Patriot Act, National Security letters were more difficult to obtain:

Under the old legal test, the FBI had to have "specific and articulable" reasons to believe the records it gathered in secret belonged to a terrorist or a spy. Now the bureau needs only to certify that the records are "sought for" or "relevant to" an investigation "to protect against international terrorism or clandestine intelligence activities." That standard enables investigators to look for conspirators by sifting the records of nearly anyone who crosses a suspect's path.

The letters do not allow conversations to be recorded. The Justice Department would have you believe they are similar to grand jury subpoenas. Here's the difference:

Grand juries tend to have a narrower focus because they investigate past conduct, not the speculative threat of unknown future attacks. Recipients of grand jury subpoenas are generally free to discuss the subpoenas publicly. And there are strict limits on sharing grand jury information with government agencies.

Gellman also tied the use of national security letters to data-mining:

[Ascroft's new] order directed the FBI to develop "data mining" technology to probe for hidden links among the people in its growing cache of electronic files. According to an FBI status report, the bureau's office of intelligence] began operating in January 2004 a new Investigative Data Warehouse, based on the same Oracle technology used by the CIA. The CIA is generally forbidden to keep such files on Americans. Data mining intensifies the impact of national security letters, because anyone's personal files can be scrutinized again and again without a fresh need to establish relevance.

Gellman reported that the FBI issued 30,000, not 9,254 NSL letters a year. And, it contracted with private firms:

Ashcroft's new guidelines allowed the FBI for the first time to add to government files consumer data from commercial providers such as LexisNexis and ChoicePoint Inc. Previous attorneys general had decided that such a move would violate the Privacy Act. In many field offices, agents said, they now have access to ChoicePoint in their squad rooms.

As I wrote here,

So when you get stopped for a traffic ticket and are told to wait in your car while the officer radios in your driver's license information, what he gets back from headquarters likely will include everything from a credit report to lawsuits you've been involved in to information about the time your neighbor called the police to complain your dog was barking too loud. Unless, of course, his squad car is equipped with its own terminal, and then he can access this information directly on the highway.

A big problem with the letters is that the Justice Department (which includes the FBI) only has to tell Congress the number of of letters issued. As Gellman noted,

In the executive branch, no FBI or Justice Department official audits the use of national security letters to assess whether they are appropriately targeted, lawfully applied or contribute important facts to an investigation.

The ACLU has been actively involved in ligitation over the use of national security letters.

Under the Patriot Act, the FBI can demand the disclosure of personal records about innocent people without getting approval from a judge. Simply by issuing a National Security Letter, the FBI can force Internet service providers, universities and other institutions to turn over customer records.

Even more disturbing, anyone who receives an NSL is gagged forever from telling anyone that the FBI demanded records. Secrecy surrounding NSLs has made it difficult for the public and Congress to know just how the FBI is using its new power.

....Our most recent lawsuit reveals that even library records aren't safe from the prying eyes of the FBI. In August 2005, the ACLU disclosed that the FBI had used an NSL to demand records from an organization that possesses sensitive information about library patrons, including borrowed reading materials and Internet usage.

Phone records, bank records, library records....in the name of the war on terror, the Government is trampling our privacy. Today it's reporters whose records are being seized and examined. Don't think you can't be next.