Officially, Microsoft stopped releasing automatic public updates for Windows XP over a month ago after over 12 years. Now a registry hack has been found that, when placed in the OS, allows it to continue receiving updates.
The hack was first reported by BetaNews and later confirmed by ZDNet. By making a few changes in the registry of XP, the hack basically tricks the automatic update servers at Microsoft into thinking the OS is Windows Embedded POSReady 2009. The OS is based on Windows XP Service Pack 3 and it will continue to get security updates from Microsoft until April 2019.
The specific registry hack works with 32-bit systems but the owners of the few 64-bit Windows XP PCs can find a workaround on this forum. However, it's more than possible that this method will be short lived as Microsoft could make changes to block any securty updates that use this hack.
It should also be noted, as Microsoft has done many times, that Windows XP is well over 12 years old and PC owners should really upgrade to a more recent version of the OS that will not only keep getting security updates but will be more secure overall.