To make this registry change, you can create a .reg file with the following contents below and execute it.
Windows Registry Editor Version 5.00 [HKEY_LOCAL_MACHINE\SYSTEM\WPA\PosReady] “Installed”=dword:00000001
Once done, the Microsoft Update website will be fooled into believing that your XP system is a POSReady system, making the latest updates available.
Thanks to ZDNet for reporting this. Unsurprisingly, Microsoft has issued a statement about the “hack” in that it is completely unsupported and that users are better off upgrading to Windows 8.1 instead. No word on if Microsoft will do anything to counter this hack, but for the time-being, XP users can gain access to the latest security updates for Windows Embedded.
SOURCE: ZDNet – Registry hack enables continued updates for Windows XP