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Out of curiosity, how can you use the URL to restrict access? After all, the script is on your server, so the URL would always be yours. So if your site was http://www.mysite.com the URL would always be http://www.mysite.com. You would never see a .edu or .org extension. If you used $_SERVER['HTTP_REFERER'] you could get the page they came from, but that would only work if the link was directly from the other site (ex: http://www.yoursite.com had a link to http://www.mysite.com/abc.php).