A hoax is a lie, told by people who know it is a lie, for the purpose of fooling other people.
The people who are pushing the Lunar Landing Hoax (the idea that the lunar landing of 1969 was a hoax) know very well that the landing was real. They don't care. Their only objective is to plant the seed of doubt in the younger generation, so that they will doubt everything that "science" tells them or that their government tell them.
It is like a terrorist action, except that it is done from the inside of the American society.
All six landings were real (Apollo 11, 12,14, 15, 16, 17) and the first one was the most watched. The Soviet Union had spy ships (Cuban fishing boats) spying on everything going on at Cape Canaveral. Amateur radio operators were able to track the Apollo capsule as it left Earth orbit, into the lunar transfer orbit (this is relatively easy to do with very simple equipment).
In 1967, two years before the 1969 landing, radio astronomers demonstrated the practical application of Very Large Baseline Interferometry, allowing radio telescopes to have MUCH better resolution than optical telescopes. The demo took place outside the USA (therefore, you cannot claim that it was a secret) and we know that the Soviets were using it before the end of 1967.
When Neil took the "small step for [a] man", the Moon was over the Pacific Ocean. It was "visible" to all the major Soviet radio telescopes. In fact, the images we saw on TV had to come through a radio telescope in Australia. So we know that the TV signal had to be visible to radio telescopes.
Not only could the Soviets tell that the signal was coming from the Moon, they could pinpoint WHERE, on the Moon, it came from.
Soon after, the Soviets did send an un-manned probe to take rock samples and bring them back. Through an exchange, they were able to compare "our" rocks with their own and saw that they were both from the same Moon, not from some Earthly lab.