Even if the eNotate software is magically unhackable, it sounds like there's no verification during the tournament that players are actually running eNotate instead of something else with the same appearance. The best way to cheat would be to write something that looks like the eNotate UI to a casual observer, but that doesn't have any of its security measures. The custom software could take the moves as it gets them and feed them into Fritz, giving hints when some secret button is pressed.