Is There a Way to Block Proxies?

I need some way to make it impossible for people working on anonymous proxies to sign up on one of my sites. However, I want to avoid blocking any other type of proxy. Is there a way to do thi开发者_JAVA百科s?

Unfortunately if the proxy doesn't send any identification HTTP headers you have no way of distinguishing between a direct request and one going through a proxy server. So there is no reliable way of achieving this.