Windows XP reached end of support on April 8, 2014 but there are many that are still harboring the old operating system on computers within the organization. We've detailed they why's behind this before and given some guidance on migrating, as well as simple mitigation steps to help avoid the thread of security breaches.
The bottom line is that you need to migrate to a newer operating system, because, ultimately, there's no measure that will keep Windows XP safe. With each passing Patch Tuesday, Windows XP becomes less and less secure, leaving open ever-widening security holes large enough to fit the ocean.
Though completely unsupported, there's a registry edit that can be made on computers running Windows XP 32-bit with Service Pack 3 that tricks the OS into thinking it's the Embedded Version of Windows XP (which is still supported until 2019).
Open up the Windows XP registry editor and create the following key structure:
Registry path: HKEY_LOCAL_MACHINE\SYSTEM\WPA\
New key: PosReady
New Dword Value: Installed
New Value Data: 1
Now, when Windows Update passes over the Windows XP computers, it will see them as "POSReady" computers and offer updates.
64-bit versions of Windows XP has a different workaround and can be found HERE.
WARNINGS: Keep in mind that Microsoft may change this function at any time (and I fully expect them to do so), so don't expect to rely on this hack forever. Also, a warning comes with this workaround. Try to keep in mind that this registry value is used to authenticate Windows embedded. Microsoft stopped testing security patches for Windows XP when the OS expired in April. This means that any newly released patches have not been tested to ensure they work properly on Windows XP and could totally trash the entire computer. So, while this seems to be a neat workaround, it may end up spelling doom for those that attempt to trust using it. And, maybe a crashed system is what some really need to get serious about migrating to a support operating system.
Keep those migrations moving!