Thank you very much! I've now turned off the generation of that ad. I swear, I looked at every one of the many settings TWICE looking for it but I see now that I didn't realize that Mail Shield and its peers had additional settings so I hadn't looked in those.
If it's default setting is off, then I'm at a loss to understand how it got turned on; I only just reinstalled Avast a week or two back after trying another product for a while. That setting was certainly off when I previously had Avast so that doesn't explain how that setting was on.