Hamachi Remote Desktop
Both hamachi and Remote Desktop open up a port to the internet to connect to. Anyone who knows the right credentials can get in.
That said, most people don't know the right credentials, and both hamachi (which is basically VPN) and Remote Desktop are both very secure. If you want to add a layer of security to Remote Desktop, you can use the principle of Security by Obscurity. Basically you would use a different port than the standard port, and whenever you connect you include that new port. This only needs to be set at the router's place for port forwarding.
For example: Port 33389 forwards to your pc's ip and port 3389.
Now from any pc, you Remote Desktop to your public ip:33389. For example: 123.45.9
Anyone who doesn't know the correct port will never know what is behind it. It is advised to make this new port any number you want as long as it is above 1023 as these are priviledged ports and have a special meaning. The ports above still have some commonly used ones, such as 3389 being the default for RDP. If you want to be totally safe, go above 10000. The highest number you can take is 65535.