“From the outset, GSM has been a system designed with stringent levels of in-built security. With constantly enhanced transmission protocols and algorithms added to the flexible and future proof platform, GSM remains the most secure public wireless standard in the world.” (www.gsmworld.com).
QRemote Control was designed to enable controlled access from within the firewall perimeter. A firewall controls IP traffic, and doesn't seem to be an appropriate tool for controlling this type of traffic.
Although the GSM device is able to act as a modem, QRemote Control simply picks up the line and drops it immediately if someone should ring the number. It only accepts GSM messages from authorized numbers. We control the device directly, and do not configure it as a Windows device of any kind, other than the serial port used to connect to the device.