so what you are saying is that pretty much every single online game in existence has not been designed correctly?
Wait what ?
I can't think of a single online game where access to the client sourcecode has an impact on security.
Yes , there are some multiplayer games that you can cheat in by modifying the client (or inspecting/modifying) the datastream but this has very little to do with the security of the game itself and sourcecode access to the client doesn't change anything.
If your game security relies on the client not being modifiable then the hackers will win unless your game is played on a trusted platform.