People were led to believe that there had been a top secret mission to mars and that they had found...... something.
Here is the faked footage featured in the show......
Despite the genesis and creation of the show being explained in detail by the people who made it, there are still many people who believe it was some kind of massive cover up/double bluff......
The mistake was in publishing a tie in book that was also written in a documentary style and not admitting it was fiction. Conspiracy theorists took to it like a duck to water, ranking it alongside other such books of the time.....