Checking where the user came from (stumbleupon) [duplicate]

This question already has answers here: Closed 11 years ago.

Possible Duplicate:

Track where users come from in PHP?

How can you check if a (unique) visiter/开发者_Go百科user was directed to your site from stumbleupon, google or facebook in php?

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Check out the referer header $_SERVER['HTTP_REFERER']