Thanks again for the help given, guys.
A quick post to round off the thread in case of benefit to Others at a later date.
Thinking about it since my reply above, I wondered if Open Candy adware might only be used to serve up options for "we recommend you also install..." during the installation process itself. Having first taken a fresh system image I therefore decided to try running the client I had already downloaded from bittorrent.com - the only Symantec message this one triggered being Open Candy - but this time with the ethernet cable unplugged from my PC during the installation process.
Bingo.
No Open Candy adware warning - and carefully searching the PC including registry finds no trace of it either. Ditto after reconnecting the network and successfully using the Bittorrent client to stress my internet connection.
Out of interest I tried the same technique with µbittorent (though I aborted installation as I didn't need it having already installed Bittorrent) and found that the Open Candy warning didn't arise here either. Open Candy therefore appears to only apply during installation and operate via a server.
Happy Chappie, especially as I proved to myself that my advertised low contention internet service is finally low contention.
