That's great that you've got a handle on things. If it becomes a problem again, you can take a necessary part of the computer (say, the keyboard) and hide it (or ask a friend to hang onto it). If the computer is in his room, and it's YOUR computer, move it to the living room or kitchen, or a room where people congregate, so there's always someone to see what he's doing. That's only if it becomes a problem again. He's an adult, and certainly should be treated as such, but a) he still has to respect your home, and b) he needs to act like an adult.