Thanks for all the suggestions guys and gals. We are going to go with and easiest/stricter approach. NO unsupervised pc time. ie, pc password changed and will stay locked unless someone is home. The pc in ? is already in the living room so it being unlocked only during hours of family occupation will solve the problem right quick.

And to touch on what a few of you had said, previously there was family trust so only 1 master account for everyone. I have to set up the computers in the house and am by know means a master at it. I dont feel that one bad egg should make me have to set up user accounts for each person (I then have to go in and help each person set up their individual settings, etc) So the bag egg just loses the privelage. Had to step back to think about it, sometimes the easiest solution just works.