Kim Philby, Donald Duart Maclean, Guy Burgess, and Anthony Blunt were among United Kingdoms counterintelligence failures as they were Soviet sympathizers in high-ranking positions in British society.
A group of Soviet sympathizers, in respected positions in British society, formed the Cambridge Five, sometimes called the Cambridge Four, and it has never been established how many active agents were involved. Of these, the most devastating was Kim Philby. Other confirmed members included Donald Duart Maclean, Guy Burgess, and Anthony Blunt. 
