I believe it's been said the leaderboards will be incorporating some sort of 'legitimacy check' in later patches. I assume they're waiting to reset them until then.
The leaderboard has no way to tell if you have modded the game. For example, one poster changed enemies to give millions of experience per kill.
Hopefully they implement an online server to play single player / leaderboards with saves kept online to have 'real' scores without people cheating/scumming
offline game with legit leaderboards probably not going to happen, people will always find a way to cheat. Only the stupid ones that go overboard with their scores will get caught.
The typical (and very easy) way to cheat most online leader boards is to just use a memory editor to change your score directly. takes all of a minute to find and change a value.
Yeah u can modify it in documents for something like killed by Chuck Norris foot. Your score -578. But for what?