Download restriction

Hello!

I am using the code below for downloading of my files.


<?
define('WP_USE_THEMES', FALSE);
require('../../../wp-blog-header.php');
$query=mysql_query("SELECT * FROM $downloadCounter_table WHERE id = '".addslashes($_GET[id])."'");
if (mysql_num_rows($query)) {
$row=mysql_fetch_array($query);
mysql_query("UPDATE $downloadCounter_table SET downloads = downloads + 1 WHERE id = '".addslashes($_GET[id])."'");
if (!dCounter_broken($row[file],1)) { header("location: $row[file]"); }
else { header("location: ".get_option(siteurl)); }
}
else { header("location: ".get_option(siteurl)); }
?>


What I want to know is how I could edit it so that only registered users will have access to the files.

Thank you.