For the Level Four challenge, there are two sources: here and here. Only the PHP code is shown here because the HTML is not important. source1.php <?php include 'connect.php'; $sql = new SQL(); $sql->connect(); $sql->query = 'SELECT username FROM users WHERE id='; if (isset ($_COOKIE['leet_hax0r'])) { $sess_data = unserialize (base64 _decode ($_COOKIE['leet_hax0r'])); try { if (is_array($sess_data) && $sess_data['ip'] != $_SERVER['REMOTE_ADDR']) { die('CANT HACK US!!!'); } } catch(Exception $e) { echo $e; } } else { $cookie = base64_encode (serialize (array ( 'ip' => $_SERVER['REMOTE_ADDR']))) ; setcookie ('leet_hax0r', $cookie, time () + (86400 * 30)); } if (isset ($_REQUEST['id']) && is_numeric ($_REQUEST['id'])) { try { $sql->query .