When "unnamed U.S. government officials" leaked the story this fall that al Qaeda computer expert Muhammad Naeem Noor Khan had been arrested in Pakistan, media reports described British and Pakistani intelligence officials as furious about the resulting firestorm of coverage. Officials were quoted as saying that the news had blown a global sting operation by destroying Khan's value as a "double agent" who'd been turned against his al Qaeda colleagues. U.S. senators and British MPs on both sides of the aisle publicly deplored this shocking intelligence "debacle."

What a terrific story. But was any of it -- Khan's purported role as a double agent, the outrage of intelligence officers -- really true? There's a good chance that much of it wasn't.

"You have to take those kinds of reports with a very large grain of salt," says Robert Vickers, a current CIA national intelligence officer and 30-year veteran of the agency. Vickers, who has participated in intelligence efforts to deceive hostile powers about agency assets in the past, notes that spreading a little disinformation is an intrinsic part of the intelligence community's culture. "We don't want our enemies to know how much -- or how little -- we know about them," he says.

The Khan story was bound to have gotten al Qaeda guessing. If Khan really was a double agent, it would be a huge blow to the organization's morale to think that a key member had turned traitor. But even if he had simply slipped up and was being monitored by both British and Pakistani intelligence, al Qaeda cells were still breached. It would make sense to spin Khan's inadvertent betrayal as a deliberate active betrayal.

Vickers won't say whether such practices have become more common in the era of Web-streamed beheadings and globally televised insurgencies, but there's no doubt that intelligence and law enforcement agencies have enormous incentive to misrepresent their successes -- and failures -- as they wage the global war against terrorists. They need to do it both to protect sources and methods and to sow confusion and doubt among the enemy. Misinformation that keeps terrorists guessing about what we know about their plans and personnel increases their uncertainty and insecurity, and that's an invaluable advantage in a war in which the enemy's identity is shrouded in shadow.

The political and operational risks associated with counterterror deception are undeniably great. The media resent being manipulated, and a government's credibility is a precious commodity. Effective deception undermines a democratic public's ability to determine how effectively, or how poorly, the war against terrorists is being run. And deception can just as easily be used to conceal incompetence as it is to protect real successes and unlucky failures.

Nevertheless, it should be used. If they're competent, intelligence and law enforcement agencies -- here and abroad -- will have already launched ongoing disinformation campaigns designed to disrupt or discontinue terrorist activities. Indeed, not to do so would represent, in the deliberately harsh words of the 9/11 commission report, "a failure of imagination."

While public disclosures of midnight captures and "treasure troves" of encrypted data on hard drives may not be outright lies, both history and counterintelligence doctrine suggest that they may not be entirely true, either. They may be embellished or played down for a very targeted audience, one that goes beyond CNN viewers or readers of the New York Times. Indeed, the CIA is legally prohibited from lying to the American media, but the prohibition doesn't apply to the agency's contacts with foreign media. The editors at al-Jazeera, al-Arabiya, Reuters and the BBC -- all outlets monitored by terrorism's supporters -- also pay attention to the rumors and reports of al Qaeda captures and alleged plots. As such, they present an excellent opportunity to deceive.

Similarly, while America's intelligence agencies generally observe policies limiting the role of deception in their media disclosures, their counterparts in the United Kingdom, France, Pakistan and Saudi Arabia do not. Before the Falklands campaign, for instance, Britain's Ministry of Defense deliberately misled the media about its intentions, a deception that contributed to the success of the surprise invasion of the islands. It's reasonable to believe that these countries may be using deception, disseminated through the media, as an integral weapon in the shadow war against terrorism.

No contemporary disinformation campaign is likely to match the strategic scale and coordination of the most famous deception campaign of modern times -- Operation Fortitude, the World War II initiative that was designed to fool the Nazi high command about the D-Day landing. With its dummy tanks and aircraft and faked radio transmissions aimed at convincing the Germans that the invasion was planned for another location, Fortitude is widely credited with delaying the arrival of Nazi reinforcements at the Normandy coast and saving thousands of Allied lives. Not surprisingly, military historians record that British and American media were involved -- some willingly, some unwittingly -- in the intricate disinformation maneuverings leading up to June 6, 1944.

Deception and media manipulation were integral to waging the Cold War, too. In the early 1980s, for example, the Reagan White House launched a targeted deception campaign to lure Soviet agents into surreptitiously acquiring cleverly reprogrammed software and silicon chips for use in the USSR's trans-Siberian oil pipeline. This high-tech tampering led directly to the pipeline's violent 1982 explosion. The administration blamed the pipeline's destruction on inferior Russian technology and shoddy workmanship, and the media dutifully reported this explanation.

To be sure, there is no foreseeable D-Day in the global war on terrorists. And non-state actors rarely have billions in targetable assets. Moreover, the media's role is infinitely more complex in an era of blogs, chat rooms and satellite TV. Yet the proliferation of media outlets -- from bloggers in Baghdad to chat rooms in Chechnya -- virtually guarantees any counterintelligence agency seeking to plant or spin a story that it will have a global reach.

In the U.S. criminal justice system, deception is a legally acceptable tactic for local law enforcement under certain circumstances. For example, courts have explicitly ruled that the police are allowed to lie and misrepresent evidence to suspects held for interrogation. Watch any episode of "Law and Order," and you're likely to see a realistic example of police misrepresenting the evidence they possess in order to elicit information.

In addition, many law enforcement agencies -- including the FBI -- often withhold from or misrepresent to the media the status of ongoing criminal investigations in the hope of tricking -- or panicking -- suspects into revealing themselves. While the prosecution is legally forbidden to spread any disinformation once a case comes to trial, manipulating the media has become an established part of pre-trial jockeying in criminal cases.

The notion that police may legally withhold and misrepresent information to catch suspected criminals while public policy precludes counterterrorism agencies from using deceptive "news releases" to thwart suspected terrorists seems foolishly -- even dangerously -- inconsistent. If al Qaeda and its affiliates operate as highly decentralized and highly compartmentalized networks of terrorist and support cells, as the intelligence community believes they do, then they no doubt face serious challenges in sharing information and coordinating activities. Any reports that create uncertainty about whether an Internet cafe might have been compromised or a cell phone tracked could postpone a planned meeting. That delay, in turn, might provoke new kinds of "chatter" for rescheduling that could make it easier to track al Qaeda's supporters. Even better, the delays might lead to outright cancellation of planned attacks.

When al-Jazeera reported, as it did this summer, that a captured al Qaeda operative has absolutely refused to say anything, and that 12 suspected militants had been arrested in London and another five detained in Riyadh, Saudi Arabia, one could imagine other al Qaeda members wondering: Did he turn or are these arrests a ruse? When the BBC reported that British and Pakistani authorities had found hundreds of names and cell phone numbers on the laptops of an al Qaeda computer operative -- but no public arrests occurred over the next month -- did that mean the report was a lie? An exaggeration? Or that surveillance was quietly underway?

Disinformation may not guarantee a victory, but it surely buys time, just as it did for the Allies in Operation Fortitude. Winston Churchill, Franklin D. Roosevelt and Gen. Dwight D. Eisenhower had the incomparable luxury of knowing how successful their deceptions were, thanks to the Bletchley Park cryptanalysts who had cracked the codes of Germany's high command. But even without such intimate knowledge of the current enemy, U.S., British and European intelligence agencies would be fools to give al Qaeda sympathizers any accurate impression of what they know. Media disinformation is thus as much a defensive shield as an offensive weapon.

Though the idea of disinformation makes free societies uncomfortable, it's likely that most Americans would understand if the government withheld some information about its counterterrorist operations, since putting it all out there would give terrorists too much knowledge of our vulnerabilities. Conversely, outright propaganda and wag-the-dog scenarios utterly bereft of fact would undermine both security and credibility.

The healthiest approach -- the one most respectful of the inherent conflict between a free press and a secure society -- is to openly acknowledge that deceiving our enemies has been and remains a legitimate national security policy. Then we can publicly debate the question of whether the operational benefits of attempting to deceive terrorists and their supporters are outweighed by the costs they impose, if uncovered, on media and governmental credibility and accountability.

America's experience with World War II and the Cold War would indicate that this is a debate where a reasonable accommodation can be made to both sides.

Author's e-mail: schrage@media.mit.edu

Michael Schrage, a senior adviser to the Massachusetts Institute of Technology's Security Studies program, conducts research on the technologies of deception in digital networks.

Mohammed Naeem Noor Khan: Do reports that he's a traitor have al Qaeda guessing?A fateful feint: Gen. Dwight D. Eisenhower sends the troops off to "full victory" on D-Day, after an Allied deception led the Germans to believe that British and U.S. troops would be landing far from Normandy.