Best advice for your situation: Assign the Windows Update service to an account (which doesn't have to exist in your Windows install [like ".\FFFFFFFFF"] ) and

Best advice for your situation: Assign the Windows Update service to an account (which doesn't have to exist in your Windows install [like ".\FFFFFFFFF"] ) and it will never succeed with updates again. You can remove the account and let it run as System if you want to restore Windows Updates functionality.