We just followed one of the ways in which we can create devices, but the security of those devices is what we are looking at. You will notice that the device ID and secure key generated for devices is unique across the millions of devices that are out in the field and registered with the IoT Hub. We can control secure keys with auto generate options as well.

Azure IoT Hub access control policies in the cloud enable the management of any device identity, providing a way to control a device from an IoT deployment as and when required. This managing of devices is based on each device identity, which is registered in the hub securely.