August 2019: John Anthony Walker, Jr. Spy Case | Federal Bureau of Investigation

On May 20, 1985, the FBI arrested John A Walker Jr, for spying for the Soviet Union. This had to have been the worst case of damage to the intel community ever.

"In 1985, dubbed by the press as the “Year of the Spy,” former U.S. Navy warrant officer John Anthony Walker, Jr. was arrested for selling U.S. secrets to the Soviet Union. Walker’s espionage began in 1967 when he walked into the Soviet Embassy in Washington, D.C., with material that would allow the Soviets to read encrypted naval messages.

During Walker’s time as an active spy, the Soviets went as far as to give him a device that, when placed on top of a cryptographic machine, would record the rotor settings, thus allowing the Soviets to decipher all communication sent using the machines. Among the information Walker provided the Soviets was naval cryptographic technology."