$file_url='file.rar';
if (strstr($_SERVER['HTTP_USER_AGENT'], "MSIE")) {
    header('Content-Type: "application/octet-stream"');
    header('Content-Disposition: attachment; filename="'.basename($file_url).'"');
    header('Expires: 0');
    header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
    header("Content-Transfer-Encoding: binary");
    header('Pragma: public');
    header("Content-Length: ".filesize($file_url));
} else {
    header('Content-Type: "application/octet-stream"');
    header('Content-Disposition: attachment; filename="'.basename($file_url).'"');
    header("Content-Transfer-Encoding: binary");
    header('Expires: 0');
    header('Pragma: no-cache');
    header("Content-Length: ".filesize($file_url));
}
readfile($file_url);