Go to advanced, then mac filtering the deny the computer. You have to know the mac address of his computer. Or just change the password on the wpa. To see who is on the wireless on the router go to the status page then wireless this will tell who is connected at that time also on the status page you can see all the ip's of the computers connected and there mac's. Also make sure that you are the only one who can access the router. Hope this will help you. M