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.