There is a common understanding the solution must have been "Honi soit qui mal y pense", which was mailed in by several gamers, but the publisher never had the intention to pay the price in the first place, and therefore never released the "official" correct answer either.
The prevailing notion is that the solution was "Honi soit qui mal y pense", submitted by several players, but the publisher did not intend to pay the price and therefore did not release the official correct answer.