help.. permission check for "last 5 posts.."

[SDB]

Hi

Could someone urgently amend this query for me to exclude posts the viewing user does not have permission to view?

$threads = $vbulletin->db->query_read("SELECT threadid, title, lastpost, lastposter
FROM " . TABLE_PREFIX . "thread
WHERE visible = '1' AND open = '1'
ORDER BY lastpost DESC LIMIT 5
");

Thanks

Simon