Throughout its existence, the UB was responsible for brutally beating, arresting, imprisoning, torturing and murdering at least tens of thousands[3][4] of political opponents and suspects as well as taking part in actions such as Operation Vistula in 1947.

The headquarters were located on Koszykowa Street in central Warsaw, but its branches and places of detention were scattered across the entire country, the most infamous being Mokotów Prison.

It was responsible for internal and foreign intelligence, counter-intelligence, monitoring anti-state activity in Poland and abroad, monitoring government and civilian communications (wiretapping), supervision of the local governments, maintaining a militsiya, maintaining prisons, fire services, rescue services, and border patrol; as well as several concentration camps set up by the NKVD (such as Zgoda labour camp).

The Red Army provided assistance to MPB not only in the form of advisors, but also with their own paramilitary units including NKGB, NKVD, GRU, SMERSH; and, in later years MGB, MVD and KGB.

[7] The first Russian chief advisor to the MPB was Major General Ivan Serov, a well-trained Stalinist experienced with Soviet security organs.

He worked as chief of the NKVD Secret Political Department, before becoming People's Commissar of Internal Affairs of the Ukrainian Soviet Socialist Republic in the USSR.

Once he became main advisor to the UB in March 1945, Ivan Serov oversaw the kidnapping of 16 top Polish politicians and underground resistance leaders, secretly transported them to Moscow, where they were tortured and thrown into jail after the staged Trial of the Sixteen.

From January 1945 (or, July 22), the surviving members of the Home Army laid down their arms, granted an official amnesty (lasting till October 15).

[13] According to depositions by Józef Światło and other communist sources, in 1945 alone the number of members of the Polish Underground State deported to Siberia and various labor camps in the Soviet Union reached 50,000.

A special disciplinary legislation had been introduced, which allowed for the sentencing of civil persons before military tribunals including young people and children.

The so-called "Cursed soldiers" of the anti-communist resistance, who opposed the new occupiers and attacked the Stalinist strongholds, were eventually hunted down by UB security services and assassination squads.

[12] The underground structures had been destroyed, and most members of the Armia Krajowa and WiN who remained opposed to communism,[13][16] were executed after kangaroo trials (staged by Wolińska-Brus and Zarakowski among others), or deported to the Soviet GULAG system.

[17] In November 1953, First Secretary of the Polish United Workers' Party, Bolesław Bierut, asked Politburo member Jakub Berman to send MBP Lieutenant Colonel Józef Światło on an important mission to East Berlin.

Światło, deputy head of UB Department 10, together with Colonel Anatol Fejgin, were asked to consult with the East German Ministry for State Security's chief Erich Mielke about eliminating Wanda Brońska.

He had also arrested and falsified evidence against Marian Spychalski, the future Minister of National Defence, who was at the time a leading politician and high-ranking military officer.

Surveillance and repressive activities were reduced; in the majority of factories, special cells of public security, set up to spy on workers, were secretly closed.

From September 3, 1955 to November 28, 1956 it also controlled the Polish Army's Main Directorate of Information (Główny Zarząd Informacji Wojska), which ran the Military Police and counter espionage service.

In 1956 the Committee was dissolved, most of its functions merged into Ministry of Interior; the secret police was renamed to the 'Security Service' (Służba Bezpieczeństwa or SB) on 28 November 1956.

The victims' bodies – often placed naked in cement bags – were wheeled out at night and buried in unmarked graves in the vicinity of various Warsaw cemeteries and in open fields.