Thanks for the link. I think I'll have to read the link a few more times before I understand it, and decide what I should do.
What's puzzling me at the moment is that the link says that the warning I referred to appears if I try to access the Intranet, but so far as I know I have not been trying to access any Intranet.
I have two external hard drives connected to my PC, but my PC is not networked in any way to any other computer.
All that I have done differently over the past couple of days is to attemt to install the Google Desktop search. Might this, in some way, be the reason for the warning.