Create a GUID.

guid.php

<?php

$guid = getGUID(array('{','}'));

print $guid;

function getGUID($strip = array()) {
    $guid = '';
    if (function_exists('com_create_guid')) {
        $guid = com_create_guid();
    }
    else {
        mt_srand((double)microtime()*10000);//optional for php 4.2.0 and up.
        $charid = strtoupper(md5(uniqid(rand(), true)));
        $hyphen = chr(45); // "-"
        $guid = chr(123) // "{"
            .substr($charid, 0, 8) . $hyphen
            .substr($charid, 8, 4) . $hyphen
            .substr($charid,12, 4) . $hyphen
            .substr($charid,16, 4) . $hyphen
            .substr($charid,20,12)
            .chr(125); // "}"
    }
    
    return str_replace($strip, '', $guid);
}

Original source: http://php.net/manual/en/function.com-create-guid.php#52354