Back in January, Microsoft added the Windows 10 Anniversary Update (version 1607) to the Volume Licensing Service Center. This started the clock ticking on the end of support for the original version of the OS, which is 1507. The date was originally set for March 26, but was eventually pushed back to May.
Now, the firm has announced the specific date after which you can no longer expect to receive security updates for the OS, and that's May 9, 2017. That date is also Patch Tuesday, the second Tuesday of the month when Microsoft releases updates for all supported versions of Windows, and 1507 will receive its final cumulative update on that day.
This is pretty significant, as it's the first time that a version of Windows 10 will end support; as it stands right now, there are four major feature updates being actively supported. For the first time, we're seeing what actually happens when a version of the OS stops getting cumulative updates.
Microsoft's solution is, you guessed it, to upgrade to a newer feature update, and to do it manually if you must. You can do so by heading over to the company's software download page and clicking 'Update now', which will download the Update Assistant.
If you don't, the firm notes that while your PC will still work, it will become "more vulnerable to security risks and viruses", since it won't receive any more security updates.