Dishonesty

Hello Nicholeen, My oldest son (14) is sneaking the laptop out out of the closet where we keep it when dad and I are out. He watches funny, silly videos with his younger brothers and then sneaks it back to its place before we arrive back home. How do I correct this? It saddens me terribly that he is not only being dishonest, but he is teaching his brothers to be dishonest too.