Not allowing to read files

I have program with data accessed by MySQL. In my assume, I copy program and its data files to my friends, and they run program with pleased faces. And now, the first friend wants to delete all program related data files and copy program related data files from second friend(or he can also get any program formatted data files) and save them into data folder. My problem: the first friend can run program with only my data files; he can get any data files from anywhere and save them into data folder, but program won't be allowed to read these data. Does everyone have some good ideads?