One month after the end of the Second World War, the Allied forces were still celebrating their victory over Nazi Germany. During the war, the Canadian forces had been part of the second - Western - front against the German forces, to relief the pressure on their Russian Allies in the east. Only four months earlier, the Americans and Soviets had shook hands when they met at the River Elbe in Germany. Many innocently believed that this ended all hostilities and that they could pick up their lives from before the war.
Meanwhile, Lieutenant Igor Sergeyevich Gouzenko had completed his second year as a cipher clerk in the Soviet embassy to Canada in Ottawa, Ontario. Gouzenko, then 26, was a member of the GRU (Soviet Military Intelligence). After returning from the Russian front two years earlier, he received training in coding and cipher work. He was sent to Ottawa in June 1943 and lived there with his wife and baby son in a small apartment. At the Embassy, he worked under GRU Colonel Nikolai Zabotin, who commanded 14 GRU officers, involved in espionage operations against Canada. Gouzenko worked in the coding room, the inner sanctum of the Embassy, where he was responsible for enciphering and deciphering of secret GRU intelligence messages between Ottawa and Moscow.
Moscow had secretly planned a complete makeover of all their communications channels. From one moment to the next, they introduced complex radio callsign and frequency schedules and all high level communications changed to the unbreakable one-time pad encryption. Every single crypto system that the U.S. had been reading went silent. Previously unencrypted channels were now encrypted and the new systems were a mystery. They no longer used the familiar crypto system indicators, leaving the eavesdroppers with no clues about who was using which system when for what messages.
It was a complete and unprecedented intelligence break-down. According to NSA, the changeover "came crashing down like a tidal wave on the beach of Anglo-American cryptology". This co-called Black Friday was a loud wake-up call. The Soviet Union had entered the battlefield of signals intelligence and it was an impressive entry. It took the National Security Agency six years to even begin to recover from this slap in the face.
The Gouzenkos were granted asylum and relocated under a new identity. Igor Gouzenko, who later appeared in several television interviews, was know for the white bag over his head that protected his identity (not a luxury, given the KGB's reputation with traitors). In 1948, Gouzenko's memoirs were published under the title This Was My Choice (see Amazon). Igor Gouzenko died of a heart attack in 1982 at Mississauga, Canada and was survived by his wife Svetlana and their eight children.
More on Igor Gouzenko is found on the Canadian Camp X website. On that page you also find Guzenko's story "Stalin sent me to Spy School", published in the Coronet magazine (direct links to each page: ). On Videofact you can read Gouzenko's statement from one month after his defection.
You can watch his famous interview on CBC Digital Archives, an interesting interview with Svetlana Gouzenko and an audio interview with his daughter Evelin Wilson. Much more video and audio are found on the CBC website by entering "Igor Gouzenko" in their search box. The Canadian Intelligence Resource Centre has some excellent papers related to Gouzenko. There, I can recommend "The Gouzenko Affair Revisited: The Soviet Perspective" (at the bottom). Various articles on the case are also found on Andrew Kavchak's commemorative page. More on the Friday black-out is found in the National Cryptologic School's On Watch document.