Cypherus.........
Thanks for your response. Since my last post I took the bull by the horns and undid the last System Restore in an attempt to follow the line of enquiry outlined by markjoy.
I then ran Norton/Symantec again which strangely didn't reveal anything untoward. Likewise Trend House Call and AVG!
I then read your post and the remark about 'Temp' files and the cogs staggered into motion. I had run Cr@p Cleaner which, amongst other things, clears these files. I suppose that was enough to solve the problem. Now, I do hope that is an end to the story!
As regards my financial transactions, yes I do back them up to an external hard drive and the really multi-mega important ones are also backed up on a USB memory stick.
Thanks again, markjoy and Cypherus,
There's a cheque in the post! (Online bank permitting)
N o t a