(CNN) — John Walker, a former U.S. Navy officer convicted of spying decades ago for the Soviet Union, has died in federal prison, according to the U.S. government.
Walker, 77, passed away Thursday at a federal correctional facility in Butner, North Carolina, the Federal Bureau of Prisons said. The agency’s website indicated Walker was scheduled to be released on parole within the year.
Authorities said the elder Walker stole, then sold, codes to help unlock encrypted Navy messages, which allowed the Soviets to monitor American military assets. The spying went on from 1968 to 1985, when he was arrested by the FBI. He later pleaded guilty.
U.S. officials later said Walker’s actions did significant damage to national security.