    function log($msg) {
        $data = sprintf("[%s] [%s] [%s] %s\n", date('r'), $_SERVER['REQUEST_URI'], (!empty($_SERVER['HTTP_REFERER']) ? $_SERVER['HTTP_REFERER'] : '-'), $msg);
        $data = strtr($data, '<>', '..');

        $filename = w3_debug_log('minify');
        return @file_put_contents($filename, $data, FILE_APPEND);
    }
The web application does not, or can not, sufficiently verify whether a well-formed, valid, consistent request was intentionally provided by the user who submitted the request.