I dont think its ADHD since he does not regret his behavior. In Adhd people become compulsive and regret their acts later on. But its important to take some steps to try to control his behavior. He seems to have no serious problems right now but discipline.Make him understand that there are so many other ways of playing the game without hurting others. Try to workaround all the options that he can find pleasureable. Set up rewards for his good behavior and some type of penality for his bad deeds. If he still continues then a child psychologist will certainly be very helpful.