Don't you just love conspiracy theories? The trouble is - they ignore basic human nature and the realities of burearcratic in-fighting. And then there's the scientific evidence. Although the gravitational forces would be identical if the moon were hollow, the angular momentum would not be the same for a hollow versus a solid sphere. This effect would be evident in the study of such things a impact craters, The differences would be subtle, but it's likely that with current instrumets someone somewhere would be able to figure out that the moon is hollow if it were. This could make someone's career, and other astronomers would rush ot confirm or debunk the data - there would be no way to keep this under wraps.
Now, going back a few decades - when NASA explored the moon, they made numerous seismic measuremetns, both with unmanned probes and when they sent astronauts. NASA would know if the moon were hollow. Imagine what this information could do for an agency about to loose the majority of its funding, having completed its mandate to land a man on the moon? If NASA had good, solid evidence that the moon was artificial, they could have requested and received funding to send even more missions to the moon, to establish one or more lunar colonies there, to drill and explore below the surface. Even if there were pressures to keep it under wraps - this wouldn't last. The various federal agencies cannot even coordinate antiterrorist activities, let alone keep such a conspiracy going.
