I'm going out on a limb and guessing you do not have a 3.55 console. You cannot "backup" games to your hard drive in that case. In addition you are pirating, you are illegally copying those games. You paid to rent it not keep a personal copy of it. You are robbing the rental company of money they could've made from you renewing the game because it took you X number of days to beat it. Basically you are stealing, we deem this as piracy.
Backing up a game is acceptable if you OWN the game and are having issues with your disc drive or you are lazy like me and hate swapping discs. The idea is that you actually own the game (not a rental).
PS: How you've come this far in life to not know what piracy is completely amazes me.