Hi,
Regarding the updates of windows defender after a jv16 powertools 2006 sweep, i found out that by entering the control panel, then selecting install uninstall programs, going to windows defender on that list and selecting it by clicking just once on it, ... there is a "modify" option that is showing up.
If you click on it, defender is showing you different options, among them :
"update". Select it and it will repair itself and additionally download the latest definition version. You may choose to perform a scan at the end.
This allows defender to be correctly updated.
I hope it helped