This is very strange. Have done full McAfee scan with no results. Also, I had forgot that "McAfee" changed my McAfee password when they supposedly cleaned my computer. I got an email stating that it had been sucessfully changed; also went to McAfee website and, using new password, was able to log into my account. Am currently running ESET scan and am going to email McAfee to see if they have record of 'cleaning' my computer (I think it was sub-contracted).

If you are still out there, Woolwell, I have at last managed to work out what has happened (McAfee have confirmed by email that they did not do this work for me) and who I contacted to sort out my firewall switching off – it was tech24x7:

http://www.tec24x7.com/techformcafee.html#mcafee

On the plus side, my firewall works fine now. Also, my hunch is that tech24x7 is kosher, though I wonder about the legality of their display/presentation (passing off??) which prominently displays the McAfee logo etc. If you read the small print at the bottom it is clear they are not McAfee; however, at first sight, (especially for anyone in something of a panic) it is easy to confuse the site for an official McAfee site.

On the minus side, I feel a bloody idiot for not checking better, am £75 lighter, and will need to change passwords, etc. A lesson to be learned. Still, once again my thanks for your help and hope this fills you in on what happened.