Security Monitor Pro broadcasts video on a specific port for each camera. You will need to open access to this port to be able to see the broadcast from the internet.

For example, the default port for the first camera is 1030. You can map port 1030 in your router to the IP address of the PC running Security Monitor Pro. Now, when you connect to your routers' IP address with mms://routerIP:1030 then Windows Media Player will open with your camera broadcast. Here is an article that explains the steps in more detail:
https://www.deskshare.com/resources/articles/wcm_Internet_Streaming.aspx