The Gatekeeper device sits between your existing firewall and the internet. It is invisible to the internet, and has no public facing IP to hack into. It completely hides designated services, such as Remote Desktop, from the internet. With the services appearing as non-existent from the internet, there is nothing for botnets to attack.
Only authorized IP addresses are allowed to see that a given port is available. The authorization process is automated using an app running on your Android or Apple phone that tracks changes to your public IP as you change locations.