It took 17 years, 7 months and 16 days to happen, but Windows XP and all of it’s variants are no longer supported by Microsoft. Windows Embedded POSReady 2009 is no longer supported as of today. This marks the end of the Windows NT 5.1 code base, which definitely makes it the oldest Windows version to have been actively supported by Microsoft. Technically, the other versions of Windows XP were not supported with Security Updates, but a registry hack allowed those patches to be installed.
Microsoft will be making changes to the encryption settings on Windows Update in July 2019 that removes the ability to install updates. So if you are still using Windows XP, for whatever reason, you have until then to perform any final updates.