Some 400,000 people worked on Project Apollo. Some spies from the former Soviet Union did penetrate NASA during this era. Most were known, the CIA preferred to keep track of known spies rather than reveal them, arrest them, only to be replaced by new unknown spies. Information did leak out to Russia regarding the Apollo technology, but nothing was ever found and exposed by them then or since the Cold War ended.
The most secret science project the USA had ever performed was the Manhattan Project; the developement of the Atomic Bomb in WW2. After the war, the CIA discovered several spies penetrated the program; Julius & Ethel Rosenberg, Klaus Fuchs and David Greenglass. The USSR built their own Atom bomb and detonated it via information from just four spies. If they were that good at spying, then why couldn't they discover the moon landings were a hoax? The answer is very simple... It wasn't a hoax!
Russia's first Atomic explosion 29th Aug 1949. Based largely on the US design that helped to end WW2. The Manhattan Project wasn't as secret as at first thought. Within four years, the Soviet Union built their own based on the plans leaked out by just four people. It would only have taken one single spy in the right place to reveal the Moon Landing Hoax. It never happened to this day.
Off coarse the hoax guys say that "Well they had secrets of their own that the USA knew about so they did a deal for both sides to keep secret." Bill Kaysing.
Both sides were spending Billions of Dollars / Rubles trying to gain something on the other risking a World Nuclear Conflict as they do... then they do a deal to avoid an embarrassment? You decide.