Counterintelligence
Counterintelligence (CI) is any activity that defends the intelligence system from enemy intelligence services.
Definition
Counterintelligence is information gathered and activities conducted to counter espionage, sabotage, etc., by (or on behalf of) foreign powers, international terrorists, etc. This broad legal definition includes offensive and defensive activities, and activities conducted within the United States or abroad.
These enemies are generally referred to as foreign intelligence entities (FIE).
Federal Regulations
Counterintelligence was first defined by Executive Order 12333 in 1981.