I agree that it will increase the security. I worded this badly. It makes cheating easier since you know how much of the stuff works. For example in one of the cheat threads a guy mentioned that the programmer of the cheat doesn't know how to move units with code without desync. Getting this to work would maybe be tedious reverse engineering work if there is no source code avaiable, but is probably very easy if he can just lookup how the AI moves in source code. Stuff like this gets much easier when the source code is available and is also nothing that opensource would improve even if it did improve actual security (such as bufferoverflows etc.).That's a myth, open-source games are not necessarily more vulnerable to attacks, instead open-source is more secure overall.
And you think they are not using version control at the moment?By how Github is designed with Pull Requests and Reviews and with setting up Continous Integration. :-)