Igor Gusenko, a Ukrainian who defected to Canada on September 5th 1945, testified and exposed the Soviet spy network operating in Canada while wearing protective clothing.

　　Ukrainian Igor Gusenko testified and exposed a spy network operating in Canada while wearing protective clothing. He stole nuclear secrets about nuclear weapons that could not be known by anyone other than a spy. Igor Gusenko, a Ukrainian who worked as a cryptographer at the embassy in Ottawa, the capital of Canada's Ontario province, defected to Canada on September 5, 1945. The Soviet Kremlin authorities carefully revitalized their espionage activities while maintaining a superficially friendly relationship with their former World War II allies immediately after the end of World War II. The Guzenko incident sparked the Cold War in the public opinion of Ottawa.

　　The FBI in Washington, the capital, uncovered Gerhard Eisler as the number one red spy in the United States. He stowed away on a Polish passenger ship and was taken off in England and interrogated. He was later extradited to Moscow. The Washington FBI also declared several American government employees, including Alger Hiss, a senior State Department official, to be subversives, and Hiss was imprisoned for perjury.

　　Ethel and Julius Rosenberg, a Manhattan machinist and the brother-in-law of David Greenglass, were involved in the development of the atomic bomb at Los Alamos. They were convicted at trial, and after an appeal to the Supreme Court, they were sentenced to death and executed in the electric chair.

　　In Russia, many people were accused of spying behind the Iron Curtain, imprisoned, and summarily executed. Two famous cases of innocent people being falsely accused were Cardinal József Mindszenty of Hungary and AP correspondent William Oatis, who was in Prague.

　　The Soviet Union's Kremlin constructed a wall along its borders, which Winston Churchill dubbed the “Iron Curtain” in his famous 1946 speech in Fulton, Missouri, USA. The structure extended along the new border, which stretched from the Baltic Sea to the Black Sea. It was guarded by the Soviet Union's Ministry of Internal Affairs (MVD) and other special forces, and physically it was equipped with watchtowers, searchlights, landmines, machine guns, police dogs and guards, and electrified barbed wire was installed across the uninhabited land. The Iron Curtain was also an ideological barrier against Western ideas.