Today is Patch Tuesday for the month of December, which means that Windows 7 has exactly one update left before its end of support. After that, the OS will be considered unsecure unless you're paying Microsoft for Extended Security Updates (ESUs). In the KB article for today's Windows 7 update, the Redmond firm outlined some things that will happen after January 14.
Windows 7 users will begin to see a full-screen warning that their OS is no longer supported, and it will stay on the screen until you interact with it. It will be included on Windows 7 Starter, Home Basic, Home Premium, Professional, and Ultimate, but it won't be on domain-joined machines or those that are in kiosk mode.
The warning won't necessarily be telling you to go and upgrade to Windows 10. Rather, Microsoft wants you to buy a new Windows 10 PC. The company says that PCs built for Windows 7 are using 10-year-old technology, and a lot has changed since then. Obviously, newer hardware is faster, and it's more secure.
Another thing that Microsoft points to is touch, something that became popular on Windows in the Windows 8 era. And oddly, the final bulletpoint is the Photos app, which makes it "easy and fun" to search for images.
The full-screen notification is part of this month's Patch Tuesday update, so if you don't want to see it after January 14, your only option is to not install the update and become unsecure a month early, which probably isn't a big deal if you're willing to run an unsecure PC a month from now.