A Windows XP registry hack that enables security updates for the OS until April 2019 has been denounced by Microsoft, which claims the patches will not protect users.
The tweak allows users to receive updates intended for Windows Embedded Industry, an operating system designed for cash machines and self-service checkouts, with much of the same code as XP.
In a statement sent to ZDNet, Microsoft said: "The security updates that could be installed are intended for Windows Embedded and Windows Server 2003 customers and do not fully protect Windows XP customers.
"Windows XP customers also run a significant risk of functionality issues with their machines if they install these updates, as they are not tested against Windows XP."
Microsoft stopped releasing security patches for Windows XP in April, prompting the British and Irish governments to hastily negotiate deals to keep public service IT systems supported.
According to NetMarketShare, as much as a quarter of computers were still running Windows XP as of April, amid concerns from security experts that three-quarters of British organisations were still using the OS on some machines.
The Windows registry contains many of the finer controls of the OS, and is mostly accessed by advanced users and system administrators looking to make minute changes to the system.
Despite fears of a security risk, many companies have opted not to migrate all of their systems, citing the high cost of moving and the dependence of legacy software on the OS.
"The best way for Windows XP customers to protect their systems is to upgrade to a more modern operating system, like Windows 7 or Windows 8.1," Microsoft added.