Sometimes you can be better by giving the exact reason.
Companies appreciate you being honest on your exit with the past company if the reason is that simple. And you can convince them the reason if they verify with your old company. If your termination is for watching banned sites within the company etc it might be difficult.
But given the situation you will be better off by giving the same reason you have been terminated for and convincing them that you will take the companies policies as sacrosanct from now on.
