Hi,
Thanks for the info. However, the 30 or so 'infections' reported have since disappeared. They were in an invisible dotSpotlite directory and in theory anyway, were all text files of caches but I couldn't open one, so I doubt they actually existed. So I ran Onynx and deleted Spotlite caches etc. Ran Avast on the entire drive and came with a bunch of embedded, mostly Windoze attachments to Word files I had from way back, which I deleted. system seems clean now, so it seems to work.
I just wonder how much of an overhead it puts on my machine (21.5-inch, Mid 2011, osx 10.9.2, 16gig ram)?