There was no issue, or certainly no security issue anyway - NSC hadn't been hacked or similar.
An existing advertiser had updated how one of their ads was going to work. I'd had prior notification, but not had time to explore the impact. When people flagged it, I removed it.
If you are getting...
If you're not logged in you could still get the ad very occasionally, but if you're logged in you should never get it. In fact I don't see how you can as I've deleted the code from the site completely.
If you do get it - please post a full screenshot so I can check it out.
I've not made any changes and have no interest in putting obtrusive ads on.
Can someone please explain what "adverts popping up" actually means in terms of what is happening so I can investigate?