The State Department issued a "worldwide caution" Thursday, warning that the newly released tape of Osama Bin Laden and a recent increase in intelligence "chatter" might indicate an imminent terrorist attack. What kind of intel counts as chatter?
When intelligence agencies monitor chatter, they examine not the content of communications intercepts, but the volume. Intelligence agencies won't define the term publicly because, they say, any disclosure might help the enemy deconstruct their methods and devise a defense. But those with knowledge of the agencies' tactics say that operatives pay attention to fluctuations in the number of messages sent and received over networks used by known and suspected terrorists. By itself, a volume increase isn't very meaningful. But when spies notice volume spikes on several networks and compare them with the content of recent communications intercepts, satellite observations, and information passed to spies on the ground, patterns emerge. In May, such patterns helped U.S. spooks zero in on Saudi Arabia as a planned target just before suicide bombers set off three blasts in Riyadh that killed 25 people and injured 200.
Spies turn to such pattern analysis because it is more reliable than individual pieces of human intelligence. Enemy defectors often provoke credibility concerns: They know that if they say what U.S. officials want to hear and are convincing enough, they may receive asylum and a lifetime pension from the government. Because chatter is a measure of collective behavior, it tends to be a fairly dependable indicator.
Intelligence agencies found it easier to monitor chatter during the Cold War. Back then, the enemy stayed in one place and used a dedicated military communications network: Everything U.S. spooks heard on these lines was military chatter. The United States could tell the Soviets were starting a military exercise whenever volume increased on the command circuits that connected missile silos to local military headquarters. But monitoring terrorist chatter is far more difficult today. For one thing, spies must contend with more numerous modes of communication—e-mails, cell phone calls, faxes, and computer data transfers among them. Complicating matters, terrorists tend to use the same circuits that civilians use. Only a tiny percentage of transmissions on these networks are useful for national security purposes, so spies must be able to identify with precision where suspects are and how they're communicating. And the advent of throwaway cell phones and computer kiosks in libraries and Internet cafes has made it possible for terrorists and others to use a different network each time they communicate, which makes them hard to track. Despite these difficulties, intelligence agencies still monitor chatter and consider it a good indicator of terrorist intentions.
Explainer thanks James Bamford, who wrote Body of Secrets: Anatomy of the Ultra-Secret National Security Agency and The Puzzle Palace: A Report on America's Most Secret Agency;Michael Bohn, a former director of the White House Situation Room; and Jim Lewis of the Center for Strategic and International Studies.