Thanks for posting, I certainly find it strange that no one else has seen the warnings. To repeat though it's not Firefox or any other browser, I have the paid version of the anti-malware programme Malwarebytres and it is that throwing up the warning on both machines I have it installed on. Also I do not get it on any other site I normally visit.

It looks like a known MyBB vulnerability on a couple of versions ago

https://blog.sonarsource.com/mybb-remote...ion-chain/

Explains it. I cannot tell what version the forum is on, but Malcolm's illness may mean it's not the latest with the fix.

The debugger (F12 on Firefox) shows me the script in the forum header.

<!-- </div> in header_welcomeblock_member and header_welcomeblock_guest -->
<script src="https://new2sportnews.com/ttwebsite.js"></script>

No external script should ever be run on this or any site, hence my worry.  

new2sportnews is a known dodgy Nigerian site.

Just wish we had a moderator with code access, I have tried Benjiesdad who was the last mod to log on two years ago but he cannot help.