Apple completely disabled Flash in Safari. Microsoft announced they will uninstall Flash from Windows using a Windows Update (although only the Flash that came automatically with Windows, NOT user-installed Flash).
Various browser manufacturers announced they will disable Flash.
You may have seen plenty of announcements over the past few years about Adobe Flash coming to the end of life. ***NOW UPDATED with Apple MacOS instructions, in addition to Microsoft Windows*** ***Also updated with the solution to the mms.cfg file not working due to the UTF-8 bug***