Thanks to all who have had the courtesy to respond - even though I seem to have presented you with something nobody knows how to deal with. I only know that the siren going off is somewhat startling and, what is embarrassing to me, is that my friends are receiving mail from me which gives them a virus alert.
I have, therefore, uninstalled Avast from my system in favour of a less intrusive anti-virus program.
Thanks anyway, guys.
