The Origins of the Cheka

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Alger Hiss is alleged to have been a KGB spy, but there is no hard evidence.

Robert Hanssen provided the KGB with information on U.S. counterintelligence efforts through his job at the FBI.

Aldrich Ames was a KGB mole within the CIA.

Ethel and Julius Rosenberg were executed by the United States for providing information on the US's atomic programs to the KGB.

James Jesus Angleton, head of CIA counter-intelligence, reportedly lived in deathly fear that the KGB had moles in two key places: CIA counter-intelligence and FBI counter-intelligence. With those two moles in place, the KGB would have control or awareness of all U.S. efforts to catch KGB spies, and could protect their assets by safely redirecting any investigation that came close, or at least provide sufficient warning; also, counter-intelligence had the job of vetting foreign sources of intelligence, so moles in that area were in a position to give a stamp of approval to double agents against the CIA. With the capture of Aldrich Ames and Robert Hanssen, it appears that Angleton's fears, deemed paranoid at the time, were well-grounded.

The KGB occasionally conducted assassinations, mainly of defectors