game_checker.rb

def save_game(file)
  score = 1000
  open(file, "w") do |f|
    f.puts(score)
    f.puts(Time.new.to_i)
  end
end

def load_game(file)
  open(file, "r") do |f|
    raise RuntimeError, "I suspect you of cheating." if f.mtime > f.atime
  end
end

save_game("game.sav")
sleep(2)
load_game("game.sav")

open("game.sav", "r+b") { |f| f.write("9") }
load_game("game.sav")