These seem to have been a bunch of false alarms. Sometimes it was a case of mistaken identity. For example, one of the “terrorists” on an Air France flight was a child whose name matched that of a terrorist leader; another was a Welsh insurance agent. Sometimes it was a case of assuming too much; British Airways Flight 223 was detained once and canceled twice, on three consecutive days, presumably because that flight number turned up on some communications intercept somewhere. In response to the public embarrassment from these false alarms, the government is slowly leaking information about a particular person who didn’t show up for his flight, and two non-Arab-looking men who may or may not have had bombs. But these seem more like efforts to save face than the very credible evidence that the government promised.

Security involves a tradeoff: a balance of the costs and benefits. It’s clear that canceling all flights, now and forever, would eliminate the threat from air travel. But no one would ever suggest that, because the tradeoff is just too onerous. Canceling a few flights here and there seems like a good tradeoff because the results of missing a real threat are so severe. But repeatedly sounding false alarms entails security problems, too. False alarms are expensive — in money, time, and the privacy of the passengers affected — and they demonstrate that the “credible threats” aren’t credible at all. Like the boy who cried wolf, everyone from airport security officials to foreign governments will stop taking these warnings seriously. We’re relying on our allies to secure international flights; demonstrating that we can’t tell terrorists from children isn’t the way to inspire confidence.

Intelligence is a difficult problem. You start with a mass of raw data: people in flight schools, secret meetings in foreign countries, tips from foreign governments, immigration records, apartment rental agreements, phone logs and credit card statements. Understanding these data, drawing the right conclusions — that’s intelligence. It’s easy in hindsight but very difficult before the fact, since most data is irrelevant and most leads are false. The crucial bits of data are just random clues among thousands of other random clues, almost all of which turn out to be false or misleading or irrelevant.

In the months and years after 9/11, the U.S. government has tried to address the problem by demanding (and largely receiving) more data. Over the New Year’s weekend, for example, federal agents collected the names of 260,000 people staying in Las Vegas hotels. This broad vacuuming of data is expensive, and completely misses the point. The problem isn’t obtaining data, it’s deciding which data is worth analyzing and then interpreting it. So much data is collected that intelligence organizations can’t possibly analyze it all. Deciding what to look at can be an impossible task, so substantial amounts of good intelligence go unread and unanalyzed. Data collection is easy; analysis is difficult.

Many think the analysis problem can be solved by throwing more computers at it, but that’s not the case. Computers are dumb. They can find obvious patterns, but they won’t be able to find the next terrorist attack. Al-Qaida is smart, and excels in doing the unexpected. Osama bin Laden and his troops are going to make mistakes, but to a computer, their “suspicious” behavior isn’t going to be any different than the suspicious behavior of millions of honest people. Finding the real plot among all the false leads requires human intelligence.

More raw data can even be counterproductive. With more data, you have the same number of “needles” and a much larger “haystack” to find them in. In the 1980s and before, East German police collected an enormous amount of data on 4 million East Germans, roughly a quarter of their population. Yet even they did not foresee the peaceful overthrow of the Communist government; they invested too heavily in data collection while neglecting data interpretation.

In early December, the European Union agreed to turn over detailed passenger data to the U.S. In the few weeks that the U.S. has had this data, we’ve seen 15 flight cancellations. We’ve seen investigative resources chasing false alarms generated by computer, instead of looking for real connections that may uncover the next terrorist plot. We may have more data, but we arguably have a worse security system.

This isn’t to say that intelligence is useless. It’s probably the best weapon we have in our attempts to thwart global terrorism, but it’s a weapon we need to learn to wield properly. The 9/11 terrorists left a huge trail of clues as they planned their attack, and so, presumably, are the terrorist plotters of today. Our failure to prevent 9/11 was a failure of analysis, a human failure. And if we fail to prevent the next terrorist attack, it will also be a human failure.

Relying on computers to sift through enormous amounts of data, and investigators to act on every alarm the computers sound, is a bad security tradeoff. It’s going to cause an endless stream of false alarms, cost millions of dollars, unduly scare people, trample on individual rights and inure people to the real threats. Good intelligence involves finding meaning among enormous reams of irrelevant data, then organizing all those disparate pieces of information into coherent predictions about what will happen next. It requires smart people who can see connections, and access to information from many different branches of government. It can’t be seen by the various individual pieces of bureaucracy; the whole picture is larger than any of them.

These airline disruptions highlight a serious problem with U.S. intelligence. There’s too much bureaucracy and not enough coordination. There’s too much reliance on computers and automation. There’s plenty of raw material, but not enough thoughtfulness. These problems are not new; they’re historically what’s been wrong with U.S. intelligence. These airline disruptions make us look like a bunch of incompetents who cry wolf at the slightest provocation.

For example, in late January 2003, the Slammer worm knocked out 911 emergency telephone service in Bellevue, Wash. The 911 data-entry terminals weren’t directly connected to the Internet, but they used the same servers that the rest of the city used, and when the servers started to fail (because the connected parts were hit by Slammer), the failure affected the 911 terminals.

What’s interesting about this story is that it was unpredicted. The Slammer attacked systems basically at random, and happened to knock over 911 service. This isn’t an attack that could have been planned in advance. It was an accidental failure, and one that happened to cascade into a major failure for the citizens of Bellevue.

I have read article after article about the risks of cyberterrorism. They’re all hype; there’s no real risk of cyberterrorism. Worms and viruses have caused all sorts of network disruptions, but it’s all been by accident. In January 2003, the SQL Slammer worm disrupted 13,000 ATMs on the Bank of America’s network. But before it happened, you couldn’t have found a security expert who understood that those systems were dependent on that vulnerability. We simply don’t understand the interactions well enough to predict which kinds of attacks could cause catastrophic results.

More recently, in August 2003, the Nachi worm disabled Diebold ATMs at two financial institutions (Diebold declined to name which ones). These machines were running the Windows operating system, and were connected to the Internet. ATM machines that weren’t running Windows were unaffected.

As mass-market computers and networks permeate more and more of our critical infrastructure, that infrastructure becomes vulnerable not only to attacks but also to sloppy software and sloppy operations. And these vulnerabilities are not necessarily the obvious ones. The computers that directly control the power grid (for example) are well protected. It’s the peripheral systems that are less protected and more likely to be vulnerable. And a direct attack is unlikely to cause our infrastructure to fail, because the connections are too complex and too obscure. It’s only by accident — a worm affecting systems at just the wrong time, allowing a minor failure to become a major one — that these massive failures occur.

Might this be what happened during the great blackout of this past summer?

The “Interim Report: Causes of the August 14th Blackout in the United States and Canada,” published in November and based on detailed research by a panel of government and industry officials, blames the blackout on an unlucky series of failures that allowed a small problem to cascade into an enormous failure.

The Blaster worm affected more than a million computers running Windows during the days after Aug. 11. The computers controlling power generation and delivery were insulated from the Internet, and they were unaffected by Blaster. But critical to the blackout were a series of alarm failures at FirstEnergy, a power company in Ohio. The report explains that the computer hosting the control room’s “alarm and logging software” failed, along with the backup computer and several remote-control consoles. Because of these failures, FirstEnergy operators did not realize what was happening and were unable to contain the problem in time.

Simultaneously, another status computer, this one at the Midwest Independent Transmission System Operator, a regional agency that oversees power distribution, failed. According to the report, a technician tried to repair it and forgot to turn it back on when he went to lunch.

To be fair, the report does not blame Blaster for the blackout. I’m less convinced. The failure of computer after computer within the FirstEnergy network certainly could be a coincidence, but it looks to me like a malicious worm.

No matter what caused the computer failures, the story is illustrative of what is to come. The computer systems we use on our desktops are not reliable enough for critical applications. Neither is the Internet. The more we rely on them in our critical infrastructure, the more vulnerable we become. The more our systems become interconnected, the more vulnerable we become.

It’s not the power generation computers, it’s the alarm computers. It’s not the police and medical systems, it’s the 911 computers that dispatch them. It’s the computer you never thought about, that — surprise — is critical and critically vulnerable.

Also during those 20 years, the NSA gradually opened its doors to the outside world. Its mission — to eavesdrop on all foreign communications of interest to the United States — remained constant throughout, but the agency that used to call itself “No Such Agency” and “Never Say Anything” started appearing in public, talking to the press and making itself known. And probably more than anyone else, James Bamford helped pry those doors open.

“Body of Secrets” is one fascinating book. It’s a secret history of U.S. foreign policy from the perspective of signals intelligence, beginning with the Cold War and continuing through the year 2000. And it’s chock-full of juicy stuff: secret Cold War missions over the Soviet Union, government coverups of military debacles, eavesdropping on our friends and enemies. Stuff you have trouble imagining a civilian being able to research and publish.

Bamford has two weapons: the tenacity needed to exploit the Freedom of Information Act and the patience to wade through mounds of public papers in archives around the country. They have both served him well.

In 1979, while researching “The Puzzle Palace,” Bamford wanted information on an NSA operation called Shamrock: an illegal program to read all international telegrams sent out of the U.S. The NSA would not respond to any queries, but he heard of a 1975 investigation by the Department of Justice. One FOIA request and nine months later, he received an impressive (and incriminating) 300-page document summarizing the program. On his next visit to the unhelpful public relations offices at the NSA, he showed people there the document. They freaked, and tried desperately to get it back.

The NSA waited for 1981 and a new president, and started applying pressure on Bamford. The Department of Justice claimed that the document was “accidentally” declassified and should be returned. (At the time, the law specifically stated that once something was declassified, it could not be reclassified, which the Reagan administration later changed.) A few tense meetings and threatening letters followed, but Bamford held firm. Shamrock was described fully in “The Puzzle Palace.”

William Friedman founded America’s first peacetime code-breaking agency — the Black Chamber — shortly before World War II and is considered the father of the NSA. After he retired he had a falling out with the NSA. He stopped trusting the agency, and it started regarding him as a security risk. At his death, he left his papers to the Virginia Military Institute and not with the NSA. Even so, NSA officials drove down to VMI, examined everything and persuaded the archivist to lock up a bunch of the documents in a vault at the institute. Also during his “Puzzle Palace” research, Bamford went to VMI to read Friedman’s papers, noticed the omissions and convinced the archivist to release those papers. He also found former NSA director Marshall Carter’s papers there; the NSA didn’t even know about them. When the NSA tried to have Bamford prosecuted after the publication of “The Puzzle Palace,” these papers were what the NSA considered to be government secrets.

“The Puzzle Palace” was a landmark book, and widely read in circles that knew something of the NSA. Inside the NSA itself, where the agency’s secrecy prevents its employees from knowing much about their own history, it was a bestseller. The book was a history of American intelligence from 1917 and was both shocking and pedestrian. Operations like Shamrock were exposed for the first time, but Bamford also spent a lot of pages simply explaining how the NSA was organized. Nobody knew anything, so it was all interesting.

Twenty years later, it is not enough to simply explain how the NSA is organized or the history of its creation. For “Body of Secrets,” Bamford issued dozens of FOIA requests and would badger the NSA every few days about them. He waded through the papers at the National Archives, the Naval War College, the National Defense University — even at the NSA’s own museum. And with the Cold War over, he found that many of the actual intercept operators — the people staffing the eavesdropping stations on ships, planes and remote corners of the planet — were willing to talk.

Among the more shocking things Bamford learned is that in 1962, the U.S. Joint Chiefs of Staff approved something called Operation Northwoods. Fortunately never implemented, it involved committing random acts of terror on Americans in the United States and then blaming them on Cuba. Most of the documents detailing this Bamford found in the National Archives, among the thousands of papers the Joint Chiefs of Staff released about the Cuban missile crisis.

In 1967, the Israeli military attacked and destroyed the USS Liberty, a spy ship that had eavesdropped on an Israeli massacre of surrendered Egyptian soldiers in the Sinai. The ship’s intercepts were destroyed, but the NSA also had spy planes eavesdropping. The details, including President Johnson’s coverup to save the Jewish vote in the next election, were in a box in the back of the NSA Museum. They were in a public place, but no one had bothered to look at them before.

In 1975, the NSA tapped the undersea cable connecting Russia’s Kamchatka Peninsula with the headquarters of the Soviet Pacific fleet. Operation Ivy Bells was the agency’s most secret operation at the time, but Bamford found the man in charge of it to be very open and cooperative.

Even the NSA was more forthcoming this time around. Bamford started asking for interviews in 1998. First it performed its usual stonewalling routine, but gradually it relented. Bamford believes that the NSA finally got the message that the book was going to be written and that it would be better off telling its side of the story. Bamford started receiving documents, getting interviews, being taken on tours. He also credits the movie “Enemy of the State” with helping to turn things around. The movie depicts employees of the NSA as black-wearing, assassinating, privacy-violating villains. Air Force Lt. Gen. Michael Hayden, the current NSA director, believes that if agency officials don’t come out and say what the agency is and what it does, then Hollywood will do it for them. Given that choice, Bamford is clearly the lesser of two evils.

The result is a book that casts the NSA in a pretty good light. It’s good at collecting intelligence, but is regularly thwarted by a government with bad intentions. In 1964, the USS Maddox was spying in the Gulf of Tonkin, off the coast of Vietnam. Believing the ship to be directing commando raids, Vietnamese patrol boats fired on the ship. Bamford produces credible evidence that this incident was deliberately provoked by the U.S. military, which wanted something that would persuade Congress to declare war. “Body of Secrets” is filled with stories like this. The book is interesting to read, well-written and scrupulously documented. Eighty-one pages of references list reports, interviews, articles. I just wish I could get my hands on Bamford’s files.

I was reading “Body of Secrets” as the current Chinese spy-plane crisis unfolded. An American EP-3 spy plane, flying a routine intelligence-gathering mission off the Chinese coast, was forced to land in China after colliding with a Chinese fighter jet that flew to intercept it. Both the Bush administration and the Jiang Zemin government postured over the incident. The Chinese demanded an official apology. The United States demanded its plane back, untouched and unboarded. Each side blamed the other. But the more you know about the history of electronic eavesdropping, the less any of it makes sense.

I don’t believe that the U.S. plane was in international waters. I don’t believe that the U.S. expects the Chinese to honor demands to return the plane untouched. (In 1976, when a defecting Russian pilot flew his MIG-25 to Japan, the Soviet Union demanded its plane back. We eventually returned it, in parts.) And I know this kind of thing is business as usual.

The United States has flown spy missions over other countries since the 1950s: the Soviet Union, China, North Korea, Vietnam, Iraq. The Soviet Union used to fly them over the United States. The target country would routinely launch fighters to harass the spy planes. This was where the Cold War would get warm, as the pilots buzzed each other, called each other names over the radio and made obscene gestures out their windows. Not all of these flights ended well. In 1956, the Chinese shot down an American spy plane in the East China Sea, killing 16. In 1968, the North Koreans shot down another spy plane, killing 31. And in 1960, the Russians downed Francis Gary Powers’ U-2 spy plane as it passed over their country. Inside the NSA’s B2 Operations Building, there is a monument of black granite with the words “They Served in Silence” and the names of the 152 military and civilian eavesdroppers who have died, most of them on ships and planes, peeking up the electronic skirts of our adversaries.

Bamford’s closing chapters are cautionary ones. Today the NSA is being flooded by a fire hose of communications, while at the same time it is being denied other communications through never-ending improvements in communications technologies. Satellites are trivial to eavesdrop on; fiber-optic cables are very difficult. The Internet has its own challenges. But most of all, the NSA’s problems lie in the difficulty of interpreting intelligence, not in the difficulty of collecting it. I have long believed that the NSA’s future lies not in intercepting communications but in targeting static databases: data at rest as opposed to data in motion. Bamford agrees.

All this makes the China incident even more confusing. I don’t understand why, in a world where intelligence satellites can eavesdrop on anything anywhere, where ground stations in Japan and South Korea have China well covered and where massive intercept programs like Echelon vacuum up almost all foreign telecommunications, we need to launch aggressive and provocative spy missions against countries like China. I can’t think of another midair collision that didn’t end up in two crashed planes; it’s a miracle that the American EP-3 survived. If the 24 Americans had died as a result of this incident, how would Congress have reacted? Would we have believed China’s claims that it was an accident, not an attack? Would we have so easily turned our warships around after the Chinese government refused our offers to assist in recovering the wreckage? How much more aggressive would the rhetoric have been on both sides? I don’t mean to imply that the U.S. deliberately set out to cause an international incident, but it seems to me that it was ignoring some pretty obvious risks for some pretty dubious rewards.

Fortunately, the plane’s crew members weren’t killed, and we didn’t have to face the kind of crisis their deaths would have triggered. But Bamford’s book explains the secret history of times when the rhetoric was more aggressive, when enemies would shoot each other down and when what the world’s leaders said in public did not match what they did in private. It’s a sobering history, and one we should take pains not to repeat.