Schneier on Security: Surveillance and Oversight:

Christmas 2003, Las Vegas. Intelligence hinted at a terrorist attack on New Year's Eve. In the absence of any real evidence, the FBI tried to compile a real-time database of everyone who was visiting the city. It collected customer data from airlines, hotels, casinos, rental car companies, even storage locker rental companies. All this information went into a massive database -- probably close to a million people overall -- that the FBI's computers analyzed, looking for links to known terrorists. Of course, no terrorist attack occurred and no plot was discovered: The intelligence was wrong.

A typical American citizen spending the holidays in Vegas might be surprised to learn that the FBI collected his personal data, but this kind of thing is increasingly common. Since 9/11, the FBI has been collecting all sorts of personal information on ordinary Americans, and it shows no signs of letting up.

The FBI has two basic tools for gathering information on large groups of Americans. Both were created in the 1970s to gather information solely on foreign terrorists and spies. Both were greatly expanded by the USA Patriot Act and other laws, and are now routinely used against ordinary, law-abiding Americans who have no connection to terrorism. Together, they represent an enormous increase in police power in the United States.

The first are FISA warrants (sometimes called Section 215 warrants, after the section of the Patriot Act that expanded their scope). These are issued in secret, by a secret court. The second are national security letters, less well known but much more powerful, and which FBI field supervisors can issue all by themselves. The exact numbers are secret, but a recent Washington Post article estimated that 30,000 letters each year demand telephone records, banking data, customer data, library records, and so on.

In both cases, the recipients of these orders are prohibited by law from disclosing the fact that they received them. And two years ago, Attorney General John Ashcroft rescinded a 1995 guideline that this information be destroyed if it is not relevant to whatever investigation it was collected for. Now, it can be saved indefinitely, and disseminated freely.

September 2005, Rotterdam. The police had already identified some of the 250 suspects in a soccer riot from the previous April, but most were unidentified but captured on video. In an effort to help, they sent text messages to 17,000 phones known to be in the vicinity of the riots, asking that anyone with information contact the police. The result was more evidence, and more arrests.

The differences between the Rotterdam and Las Vegas incidents are instructive. The Rotterdam police needed specific data for a specific purpose. Its members worked with federal justice officials to ensure that they complied with the country's strict privacy laws. They obtained the phone numbers without any names attached, and deleted them immediately after sending the single text message. And their actions were public, widely reported in the press.

On the other hand, the FBI has no judicial oversight. With only a vague hinting that a Las Vegas attack might occur, the bureau vacuumed up an enormous amount of information. First its members tried asking for the data; then they turned to national security letters and, in some cases, subpoenas. There was no requirement to delete the data, and there is every reason to believe that the FBI still has it all. And the bureau worked in secret; the only reason we know this happened is that the operation leaked.

These differences illustrate four principles that should guide our use of personal information by the police. The first is oversight: In order to obtain personal information, the police should be required to show probable cause, and convince a judge to issue a warrant for the specific information needed. Second, minimization: The police should only get the specific information they need, and not any more. Nor should they be allowed to collect large blocks of information in order to go on "fishing expeditions," looking for suspicious behavior. The third is transparency: The public should know, if not immediately then eventually, what information the police are getting and how it is being used. And fourth, destruction. Any data the police obtains should be destroyed immediately after its court-authorized purpose is achieved. The police should not be able to hold on to it, just in case it might become useful at some future date.

This isn't about our ability to combat terrorism; it's about police power. Traditional law already gives police enormous power to peer into the personal lives of people, to use new crime-fighting technologies, and to correlate that information. But unfettered police power quickly resembles a police state, and checks on that power make us all safer.

As more of our lives become digital, we leave an ever-widening audit trail in our wake. This information has enormous social value -- not just for national security and law enforcement, but for purposes as mundane as using cell-phone data to track road congestion, and as important as using medical data to track the spread of diseases. Our challenge is to make this information available when and where it needs to be, but also to protect the principles of privacy and liberty our country is built on.

This essay originally appeared in the Minneapolis Star-Tribune.

(Via Schneier on Security.)