Sending game version to server to check for updates: How do I prevent manipulation of game version?

I'm building a game and want it to be as secure as possible because it involves cryptocurrency. A scenario I think about is if a user happened to find a bug or exploit in the game. I want to make sure I can deny access to the user if he's still using an old build. My first draft of the process was like this: - user starts game - title screen scene opens - web request sent to server to get allowed game/build version - if both match, server sends response to allow player to log in - if failed, prompt tells users to update their game - Of course this is flawed because if a user decides to download the current version on another device, copy it and send it to an old build they'd bypass the validation. Even if the version is encrypted, they'd still be able to access it on a new game build and send it to the server.