Someone

function getIP() {
	# list of bad IP patterns proxies (which could inflate stats) from RFC1918
	$badips = Array("^127.","^10.","^172.16.","^172.17.","^172.18.","^172.19.","^172.2","^172.30","^172.31","^192.168.");
	if(isset($_SERVER['HTTP_VIA'])) {
		if(isset($_SERVER['HTTP_X_FORWARDED_FOR'])) {
			$x = 0;
			while(!isset($ip)) {
				$badip = $badips[$x];
				# if the proxy is serving private IP blocks, it's probably a legit company firewall.
				# log the proxy IP address and give them credit. it's assumed they can't cheat since
				# the IPs behind the proxy will be private.
				if(ereg($badip, $_SERVER['HTTP_X_FORWARDED_FOR'])) {
					$ip = $_SERVER['REMOTE_ADDR'];
				}
				# if the proxy isn't serving private IP blocks, consider it legit.
				if($x == count($badips)-1) {
					$ip = $_SERVER['HTTP_X_FORWARDED_FOR'];
				}
				$x++;
			}
		} else {
			# anonymous proxies don't pass the X-Forwarded-For header.
			$ip = "";
		}
	} else {
		# no proxy.
		$ip = $_SERVER['REMOTE_ADDR'];
	}
	return $ip;
}