Hi thanks for the replies.
I could not see the folders Avast was referring to even with show hidden files & folders + show system files enabled so I could not point an on-line scanner at them.
But anyway it does not matter because even though Norton was uninstalled just after the laptop was last reformatted (it is part of IBM's image) and so does not appear in add & remove programs or program files or Common Files when I ran the latest Norton removal tool it seemed to spend ages un-installing something the processor light was working over time
I then rebooted, emptied system restore & did a thorough scan including archives with Avast & Hey Presto it was clear (apart for a load of files it could not open which seems par for the course for most scanners)
Thanks for your help!