Is it standard to check for proxies with getenv and is it effective?

Hey quick question, I am wondering

1. Do big sites use php's getenv function to prevent proxy users from registering or signing in?
2. Is it effective in deterring hac开发者_如何学Ckers from creating a bunch of accounts for abusive purposes if it is used?

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There is no 100% effective way to determine whether a given user is utilizing a proxy or not. It's generally fairly ineffective to try - plus you'll block many legitimate users in the process.

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I don't believe getenv would be helpful at all in doing this (unless combined with some ugly flash applet). getenv() returns the remote address that's directly connected to the webserver (I think), which may or may not by the user's IP (i.e. they could be behind a NAT). I also don't believe this would be effective at all to prevent people from using proxies.