In the 90's, if a developer made a game with a cheat code that was 'exclusive' to buying a particular strategy guide, would it be unethical to share/use that ch

In the 90's, if a developer made a game with a cheat code that was 'exclusive' to buying a particular strategy guide, would it be unethical to share/use that cheat code without buying your own copy? I don't think so.