Hello again everyone,
Thankyou for all your helpful replies. I downloaded the EWIDO software, and the scan found two trojian viruses on my system. These have now been removed, and everything is working normally.
I am at a bit of a loss to understand why my AVG anti virus could not prevent this trojian from reappearing- I keep it up to date.
Anyway, the main this is that the nasty has been removed. My friend keeps telling me to get a Mac - they are not as prone to virus attack.
Regards,
David
England, UK.