Thanks BOAC - I did read your post 4, but as far as I can see, Avast does not give me the option to quarantine the virus. It just tells me that the virus has been placed in the 'chest' and that no further action is required.
I have 'Spyhunter' installed, and am not sure if Malwarebytes would be of any extra help, as the virus is not actually 'in' the PC as Avast has prevented it taking hold.