I am using a d-link dsl-320t modem with the security enabled and ZoneAlarm free on PC's. When I do a Shields-up test it exposes some ports to the internet but the ports are closed. A test with ZA and a PC using another modem shows all ports shields up and so it must be the firewall in the modem. I am sure it is possible set up the NAT firewall to hide these ports but does anyone know how to do it. The manual is hard going and pretty useless.