"Have you ever lived in Oregon?" he asks.

Talk about anomalous data: I've been to Europe about sixty times. I've been to the Middle East, Africa, Asia. I've never been in the state of Oregon. If the U.S. government is serious about building the meta-databases that it purports will be the counterterrorist tools of tomorrow, they will have to have more robust software than this.

"Sorry," I say. "Never even been there."

Judging from the travel promotions I've been getting since my return—via e-mail and snail mail—my credit card providers have clearly been convinced that my movements through London, Berlin, St. Moritz, and Milan have created a body of predictive demographic information about me. They would be right about an ordinary traveler, but in my case they're wrong. This trip was journalistically determined. I pretended to be a recreational traveler, much as a terrorist would operate under civilian cover. Ergo, my patterns will yield less-accurate marketing information.

This deceptive scrim over my actions also spells trouble for counterterrorist agencies, police, and border authorities around the globe that depend on the analysis of personal data to determine my intentions, or, more precisely, the meaning of my patterns.

Had I been, say, an unarmed intelligence gatherer for a terrorist cell, my pretense of recreational travel would have been highly successful. Hardest of all to detect are the malicious intentions of people whose documents, credit cards, and personal histories appear to be spanking clean. Many legitimate, ordinary people share the same patterns of purchasing, countries of origin, cell phone providers, and banks as those used by terrorists. Governments worldwide are betting that building data banks of unimaginable size and felicity will help single out those among us who might harbor malicious intent by matching, let's say, a U.S. visa issued in Malaysia, with a truck rented in Montreal, and a purchase of ammonium nitrate in Upstate New York.

Any data registry—digital or analog, civil or official—suffers a real-time lag between data collection and the point at which the information yields its meaning, or becomes "known." Organized-crime kingpins, terrorists, and lowly flimflam artists all exploit this lag. If the gap is too great, data that has law-enforcement relevance cannot be acted upon in time. Former White House counterterrorism coordinator Richard Clarke's powerful apology to the families of 9/11 victims and his subsequent testimony before the Kean Commission was a data analyst's diagram of how a government does not know what it knows. To prevent this sort of lapse, the CIA, the FBI, the Department of Homeland Security, and the Defense Department have formed the new Terrorism Threat Integration Center, a sort of central data-distributing apparatus—in effect, a brain telling various arms of the U.S. government what is known. Under debate in the White House and in Congress is a new post that would bring the Pentagon's eight intelligence agencies, the CIA, the FBI, and the intelligence arms of the departments of State, Energy, Treasury, and Homeland Security under one über-czar of knowledge. It is our government's attempt to live up to the maxim, Know thyself.

Back in my local coffee shop, two French neighbors, Elise and Julie, arrive with a cat in a carrier. The cat's name is Yoda, and she is slightly freaked out. She's just come from the vet, where she's had a subcutaneous radio-transmission identification chip implanted in her rump. The reason is that Yoda, who has been issued a French "pet passport" in order to enter the United States, is returning to Paris with Julie. According to French regulations, in order to bring an animal into the country it must have a chip. This technology, developed to help identify lost pets, has become a trusted device to register animals at national borders. About the size of a grain of rice, the chip is reportedly difficult to remove or manipulate.

Elise and Julie are entertained by all of this. They find it stupid but, once done, sort of practical.

"Think how convenient it would be," says Julie, trying to calm the cat down through the carrier door, "if we could just implant these things in people."