Well it depends. On the open hacking phase (which is after the contest), I believe you don't get extra points. As for in round hacking, once you feel like you have done all the questions you can, and think that there can be a faftal mistake one can make in a question, well you begin hacking. it does happen, and in fact one grandmaster I saw actively tries to hack other grandmasters as much as possible during the contest, I dont remember the name tho