I remember a few years ago when my dad tried to block my brother and I out of his PC when he wasn't home with BIOS passwords.... Little did he know that it had a default password, so I logged in using it everytime he wasn't home. Never told my brother either
Eventually he caught on, so he used a a keylock... if I was real desperate I would open the case and hard wire the connection together for the lock to login. Only did it a couple times. I do feel guilty now, but then again, I'm now a software engineering/comp sci student, my grades are up, I don't think my dad is too angry that I messed with it back then now
Mind you, when I do have my own kids, I'll more than likely try to limit my children's access times to the PC when I don't want them on. My dad always said I'd turn into him someday, lol, he was right!