I access this forum via an IPad with which I have the Norton security app installed and from time to time I get notifications saying that this forum is not secure, please advise?
It seems a bit vague. Don't these notifications offer further details?
You can scan this site (or any other) here to check on the security:
https://www.ssllabs.com/ssltest/
Here is a screenshot of the Norton security report. I think it is to do with the advertisements on this forum?
Many of the videos posted in this forum come with dodgy ads, so when you receive one of those notifications it may have been triggered by a video.