Thanks CSL.
As you probably know, from your end, I use Opera. No add-ons, and I use a private browsing window for things like SD so hopefully clean of any cookies etc. at start of session.
It was a clean install (along with the complete laptop) in February. Nothing added and some changed settings by me to further tighten security. Opera is nowadays based on Chromium, and I highly recommend it, for many reasons.
Currently on
Version:76.0.4017.107
Restart Opera to update to version 76.0.4017.123
So Opera, and the whole PC, will be getting a full restart later today.
I fully restart my PC once a week, whether it needs it or not, to ensure MS and other updates go in.
The Avast AV is up to date, but on further research this virus, if that is what it was, and not a false positive, seems to be trying to mess with a component of Avast itself, the part that intercepts my e-mail programs to check inward and outward e-mail, neither of which programs (MS mail and Eudora) were running at the time. Though of course MS mail may be doing stuff in the background, even when not open.
Windows Defender is also running alongside Avast.
I merely flagged it up because the alert popped up a second or so after I opened a page on SD. Which was perhaps just chance. The URL being
Fancy fuels.
I have the thing stored in the virus vault, so could perhaps get it out and send it to you in an encrypted zip or 7-zip archive, if you are interested.
TBH I am more inclined to think that it is something to do with Avast itself, its database, and it's Behaviour Shield.