Fully anonymous proxies. Such proxies do not change request fields and look like real browser. You real IP is also hidden of course. People that administrating internet servers will think that you are not using any proxies. HTTP Servers of this type does not send HTTP_X_FORWARDED_FOR, HTTP_VIA and HTTP_PROXY_CONNECTION variables. Host doesn't even know you are using proxy server an of course it doesn't know your IP address.