I just want to thank everyone who offered a suggestion or advice on fixing my problem. It (they) were much appreciated.
I wrote to Trend Micro about this particular virus (if it is indeed a virus but didn't get any responses) so I'm assuming it was probably a heuristic virus and has since be fixed in one of their updates. Whatever the reason, the pop-up from Trend Micro no longer appears.
I've also figured out how to scan the correct registry when required, again, thanks to your help.
