According to Neil Armstrong the Aliens have a base on the Moon and wanted us to get off and stay off the Moon! Milton Cooper a Naval Intellegence Officer tell us that the Intellegence community calls the Alien Base "Luna":

LUNA: The Alien base on the far side of the Moon. It was seen and filmed by the Apollo Astronauts. A base, a mining operation using very large machines, and the very large alien craft described in sighting reports as MOTHER SHIPS exist there.
- Milton Cooper

...

A certain professor, who wished to remain anonymous, was engaged in a discussion with Neil Armstrong during a NASA symposium.

Professor: What REALLY happened out there with Apollo 11?

Armstrong: It was incredible, of course we had always known there was a possibility, the fact is, we were warned off!(by the Aliens). There was never any question then of a space station or a moon city.

Professor: How do you mean "warned off"?

Armstrong: I can't go into details, except to say that their ships were far superior to ours both in size and technology - Boy, were they big!...and menacing! No, there is no question of a space station.

Professor: But NASA had other missions after Apollo 11?

Armstrong: Naturally - NASA was committed at that time, and couldn't risk panic on Earth. But it really was a quick scoop and back again.

Armstrong confirmed that the story was true but refused to go into further detail, beyond admitting that the CIA was behind the cover-up.