Markus Hess hacks on behalf of the KGB
A German citizen recruited by the KGB to spy for the Soviets in the 1980s, Hess broke into 400 U.S. military computers in order to obtain in classified information, including the OPTIMIS Database at the Pentagon.
His activity was eventually detected by Clifford Stoll at the computer center of the Lawrence Berkeley Laboratory (LBL) in California. Hess was found guilty of espionage and sentenced to one to three years in prison. Stoll wrote about the experience in a book titled “The Cuckoo's Egg.”