To what end? I guess they could troll your "mobile app installation counter" if they really want to, but so what?
If someone wants to misrepresent how many times they've installed your app, there's nothing you can do about it. (They could just uninstall then reinstall over and over.)
Though... obviously they should only be able to mess with their own statistics, not the global statistics.
True that there's nothing terrible they can do when it's just statistics. The obvious solution would be to remove the global variables altogether, so that each user only has their own (from which the global versions are calculated).
That way, if the user was to do stupid things to their own variables, they could just be removed when calculating the global ones.
If someone wants to misrepresent how many times they've installed your app, there's nothing you can do about it. (They could just uninstall then reinstall over and over.)
Though... obviously they should only be able to mess with their own statistics, not the global statistics.