With linux you can issue a certificate and put it into putty and disable password login.
I think this is a great way to stop pesky bots hammering RDP login the whole time.
I have noticed on the Start SSL website, they generate a certificate for you, which gets installed onto your browser and you don't need to type in a password to login, as long as you have that certificate in the browser.
Is it possible to connect to RDP using certificate authentication from the client?