[akanevsky]

Okay, you got some excess queries and code here...

There is no reason behind veryfind referrer's id, because it is already verified by vBulletin... All you need to do is this:

After

PHP Code:

 if (!$testreferrerid = $DB_site->query_first("SELECT userid FROM " . TABLE_PREFIX . "user WHERE username = '" . addslashes(htmlspecialchars_uni($_POST['referrername'])) . "'"))
 {
    eval('$errors[130] = "' . fetch_phrase('badreferrer', PHRASETYPEID_ERROR) . '";');
 } 


Add

PHP Code:

    else
 {
    $DB_site->query("
        UPDATE " . TABLE_PREFIX . "usertextfield
        SET buddylist = TRIM(CONCAT(buddylist, ' ', '$testreferrerid[userid]'))
        WHERE username = '" . addslashes(htmlspecialchars_uni($_POST['referrername'])) . "'
    ");
 } 


And this

PHP Code:

 if ($referrer)
 {
    // Put it in the database.
    $DB_site->query("
           UPDATE " . TABLE_PREFIX . "usertextfield
           SET buddylist = '" . addslashes($testreferrerid[userid]) . "'
           WHERE userid = $userid
    ");
 } 


Should be replaced by

PHP Code:

    if ($referrer)
 {
    // Put it in the database.
    $DB_site->query("
        UPDATE " . TABLE_PREFIX . "usertextfield
        SET buddylist = '$testreferrerid[userid]'
        WHERE userid = '$userid';
    ");
 } 


Oops, looks like I have rewritten your hack. Oh well.. :P