Follow up to my posting which may be of interest to others using AVG. An update on 10.3.10 apparently caused the default exclusion of archive files (zip, rar, etc) which almost certainly explains the better speed fewer scanned objects effects. Not sure why it didn't show up until 17th. I think I agree with this change as you are probably only going to be affected by an embedded nasty if you expand the archive but it would have been nice to have been told. I expect I should have used the paid for version!!
Tony