Possibly this: From their website: Normally websites you visit will not see your IP address, but if WebRTC is enabled, your IP may be leaked by WebRTC. Google Chrome does not allow users to disable WebRTC. If this is a concern for you, you may install a Chrome extension that prevent this. Here is one example: Easy WebRTC Block. Since Ultrasurf uses Chrome in incognito mode, you need to allow it in incognito mode (enter “chrome://extensions” in address bar, click “Details” on “Easy WebRTC Block” and enable “Allow in incognito”)