Learning from a classic ...

... War Of The Moles: The Lessons of Le Carre. (Hat tip, Dave Lull.)

These double agents came to light largely because of the defections from the KGB that followed the fall of the Soviet Union. Unfortunately, under more normal circumstances, entrenched bureaucracies can be expected to resist reappraisals of their past work, especially where careers are at stake. The intelligence community's 2007 National Intelligence Estimate (NIE) on Iran is a case in point.