The issue happens when I'm not logged into my account and access Sims 4 Downloads for the first time. There is a large transparent banner that overlaps the clickable buttons for Build Mode, Game Mods, Buy Mode, etc. When I click on them I'm redirected to an offline site that Norton immediately closes due to harmful content. I haven't been able to repeat the situation since logging into my account.

Not sure if this sequence helps, but ...
- Open Browser when not logged in
- Go to MTS Sims 4 Downloads page
- Click any of the buttons
- Sent to a harmful site
- Close that pop-up
- Browse downloads as normal.

Weird. I'm not getting this, but you are not the first person reporting something similar in the past couple of months. Are you able to repeat the problem?

Can you give us the address of the page that first presents the issue?

Also try posting your findings in: http://www.modthesims.info/forumdisplay.php?f=24

I highly recommend you install a Malwarebytes from www.malwarebytes.org and run a scan.

There are a few ways malware, hackers, and even your own Internet Service Provider can inject ads into your internet traffic.