you sound like someone who has no idea what hes doing... maybe that's why you were using TeamViewer.
if you need to use remote desktops across the internet, or any network, to either offer support or access a remote PC, then you should have been using SSH.
you can open an SSH tunnel to a host, then forward all local connections to a local proxy which then leads to the host. (you can do this with putty)
that way you can be on the same network as your host and use SFTP, terminals, remote desks, whatever the hell you feel like.
you can use free options for SSH on winblows, Bitvise ssh is pretty damn impressive and even if you don't use their server, the client they have is by far the best SSH client you'll ever find. and has a built in RDP controller that will handle the forwarding of the connection.
keep in mind you are not supposed to use their server for commercial uses (but you can if you have no morals), but the client is fair game. if you need an alternative server for free:
github.com/PowerShell/Win32-OpenSSH/releases
which is still on beta, but on a very active development.
as far as security goes, nothing comes close to a properly set up SSH server. you can have layers upon layers of security, from Key only access, rolling passwords, obfuscation, dummy logins, whatever... there's no way the ruskies are getting in.
stop being retarded and read up on SSH tunneling.
Attached: ssh.png (256x256, 4K)