Robert Hannsen is a traitor who was arrested on February 18, 2001. Hannsen spied for the Soviets and later Russia against the US for at least 15 years. He pled guilty to 15 counts of espionage and sentenced to life in prison. His treason has been described as one of the worst intelligence disasters in US history.
Hannsen is responsible for numerous Soviets working for the U.S. being executed. In 1985, he exposed 3 KGB agents working for the U.S. They were recalled and executed by the Soviets. On two occasions, Hannsen gave the Soviets a list of all American double agents, people whose job it is to pass misinformation to the Soviets. He also revealed a secret tunnel dug under the Soviet embassy for the purpose of eavesdropping. He compromised the investigation of Felix Bloch, a State Department official accused of working with the Soviets.
Hannsen sold the Soviets super secret software called Promis. This software is equipped with artificial intelligence and can analyze tens of millions of snippets of information in seconds that can both identify and predict the actions of a target. This software was later sold to Iran and recently turned up in Iraq in the hands of the radical cleric, Moqtada al-Sadr.