Federal Security Service
The Federal Security Service (Russian: Federalnaya Sluzhba Bezopasnosti)[1] formerly (1994–95) Federal Counterintelligence Service, Russian internal security and counterintelligence service created in 1994 as the successor of the Soviet-era KGB's domestic criminal and counterintelligence functions. It's sister agency, the SVR, took over foreign intelligence, on the American model of dividing the FBI's domestic functions from the CIA foreign covert action and intelligence gathering mission.
Vladimir Putin has been known to employ the FSB in many of the same ways as the old KGB.[2]
FSK
Following the collapse of the Soviet Union, the KGB was transformed into the FSK, or Federal Counterintelligence Service. (Federalnaya Sluzhba Kontrrazvedki) The FSK existed from 1991 until 1995, when it was transformed again into the FSB.[1]