So long as there's significant penalty to participating as a seller in this market for those actually writing the software then I don't see why it can't be public. I don't think it would be a good idea to allow without penalty someone who is writing the software to be cashing in on million+ dollar bonuses for back doors he writes himself however. That seems analogous to insider trading.

Forfeiture of all money gained as such and a stiff jail sentence should be enough to discourage any but those who are already doing this without public knowledge of the market.