AP Photo

When the Cold War ended, the work of America’s intelligence analysts suddenly became vastly more difficult. In the past, they had known who the nation’s main adversaries were and what bits of information they needed to acquire about them: the number of SS-9 missiles Moscow could deploy, for example, or the number of warheads each missile could carry. The U.S. intelligence community had been in search of secrets—facts that exist but are hidden by one government from another. After the Soviet Union’s collapse, as Bruce Berkowitz and Allan Goodman observe in Best Truth: Intelligence in the Information Age (2002), it found a new role thrust upon it: the untangling of mysteries.

Computer security expert Susan Landau identifies the 1979 Islamic Revolution in Iran...