HTML (Hypertext markup language) is the code in which sites are written (said the non-expert) and forums, too.
GB doesn't use HTML for the forum.
It uses UBB (evidently another type of code) instead.
So, it's really nothing for you to be worried about.
You probably do have Adobe Flash on your computer, Richard.
I have it on mine.
It's pretty much a standard thing.
You can check under Add/Remove programs to see if it's there.
Edit: Come to think of it, one of my games from GOG is a flash game: The Ballads of Reemus.
Without the flash plugin, I couldn't play it.
It's goofy but fun and since I got it on a Deep discount, I'm not complaining.
Btw, Richard, the ads are annoying (which is why so many of us block them) but those companies aren't responsible for the malware that can be distributed with them.
The bad guys have figured out a way to piggyback on legit ads (at least that's what I got from the report) and hit your computer through them.