The original RTM version of Windows 10 was released on July 29 back in 2015. Since then, Microsoft has released 3 major updates for the Windows 10 platform, including the recently released Creators Update (version 1703). At the same time, the original Windows 10 has received a bunch of cumulative updates, including security fixes and stability improvements. However, Microsoft is now supporting its frequently updated products for 18 months or 1.5 years, and the time for Windows 10 ver. 1507 support to end is almost up.
The original plan to drop support for Windows 10 RTM was supposed to happen at the end of March 2017, but the date was pushed back to May 2017 to allow enterprise clients to migrate their devices in time. This being said, all 4 consumer SKUs of Windows 10 (Home, Pro, Enterprise and Education) will no longer receive any updates after May 9, 2017. Users will have to upgrade to one of the newer Windows 10 versions to continue receiving new bug fixes and improvements.
After May 9, 2017, Windows 10 devices running version 1507 will no longer receive security and quality updates. Microsoft recommends updating devices to the latest version of Windows 10 by visiting the Software Download site and selecting Update now to manually update your device.
Running the older version of Windows 10 after that date may allow hackers to potentially execute harmful code on your devices via newly discovered yet unpatched security holes. So if you're concerned about your security, don't forget to upgrade to the latest version of Windows 10 before May 9, 2017.