I have an Acer laptop with windows 8 OS. I have Avast anti virus free. as security.
The laptop is seldom used and I switched on to update and thought I'd run a scan. Avast came up with several rootkit infections that it would not let me delete. It then told me that it had an important update and said it needed to do a boot scan. I allowed it to do that and then it updated.
I have since run another scan and it has found nothing apart from it being unable to scan a google toolbar.