Ahh, preventing online cheating with scores is easy. What you do is store the score twice, once calculating the score in memory (to be displayed on screen) using normal scoring techniques and then secondly to be scored in a totally different way using variables and stuff (maybe not even using numbers at all)
That way it doesn't matter what your score is, the password is being made from something totally different and will be very difficult to know how. It also means if someone overwrites the numbers in memory to make a huge highscore (easy peasy) it won't make a difference because when the score is made into a passcode, it makes no difference because the code is being generated elsewhere, the numbers really are just dummy numbers.
You should also make it when a player tries to upload their new score that you make it so you have to check the numbers yourself. This stops someone continually testing and trying to break your code against the server.
That way it doesn't matter what your score is, the password is being made from something totally different and will be very difficult to know how. It also means if someone overwrites the numbers in memory to make a huge highscore (easy peasy) it won't make a difference because when the score is made into a passcode, it makes no difference because the code is being generated elsewhere, the numbers really are just dummy numbers.
You should also make it when a player tries to upload their new score that you make it so you have to check the numbers yourself. This stops someone continually testing and trying to break your code against the server.