AVG is on permanently and does a full check every day. The full check takes about twenty minutes and finds something no more often than once a year. I run Adaware every two or three days and it typically finds between one and three "critical" - but they're not, really - items each time. They're usually cookies which are there because someone else in the family has been running their favourite browser with cookies allowed. I don't allow cookies on my day-to-day browser.
I'm following your advice on the clean-up at the moment on my computer and 'll tell you how I get on. Thank you, once again.