Something

		$referer = array("www.2checkout.com", "2checkout.com", "www2.2checkout.com" );
		
		while( list($key, $val) = each($referer)) {
			if (strstr($_SERVER['HTTP_REFERER'],$val)) {
				$grant = 'true';
			} // End giving grant a value
		} // End while
		
		if($grant != 'true') {
			echo "<h3>You seem to came back not from 2checkout</h3>";
			return;
		}