 Several other factors contributed to the destabilization of Poland.These included the widely publicized defection in 1953 of high-ranking Polish intelligence agent Józef Światło, resulting in the weakening of the Ministry of Public Security of Poland (Polish secret police).In addition, the unexpected death in Moscow in 1956 of Bolesław Bierut, the PZPR First Secretary (known as the "Stalin of Poland"), led to increased rivalry between various factions of Polish communists and to growing tensions in Polish society, culminating in the Poznań 1956 protests (also known as June '56).