By secretly making requests to our STUN servers then log your request. These requests do not show up in developer consoles and cannot be blocked by browser plugins -- they are undetectable by the user -- unless I want them to print on the page >:O) . STUN servers are used for VOIP, IM (jabber skype etc) and WebRTC
- I get the user's local router address (LAN NAT) e.g.; 192
- his real IP address
- listed under his proxy or vpn IP address
80% effective
That is how a proxy or VPN works in the end -- the real address is in the IP packet header.