A reprint from the PC410 Security Newsletter:

The lock screen is that first photo that Windows shows on startup, with the login prompt. It shows advertising occasionally, usually for Microsoft Games, and suggests a visit to the Microsoft store, or asks odd questions. That’s an odd location for any of that; they probably got the idea from the Amazon “Kindle with Special Offers”, which does something similar.

To turn off these annoyances, go to Settings, Personalization, Lock Screen, and change the top item, to either Picture or Slideshow. “Windows spotlight” is the setting that shows ads. After making that change, set “Get fun facts, tips, tricks, and more on your lock screen” to Off. Important: This setting is reset by installing some of the larger Windows 10 updates, so re-apply as needed. Bad news if you aren’t running the ‘Pro’ version of Windows: Not all settings of this type are available for ‘home’ users.