I have an internal server that hosts an asp.net intranet application. I want to keep it completely and utterly secure and private however we need to expose some information through a WCF service to another server which hosts our external websites which CAN be accessed by the public. What is the best way to pass information between the two servers with regards to an IT setup, while keeping the intranet in house server completely secure and inaccessible? I've heard VPN was the way to go but I wanted to be sure this was the safest way.

Another question what would be the most secure way of passing data in the WCF service?