

“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,” the company said in May. Of course, Microsoft advises against Windows XP users installing these fixes, and suggests updating to Windows 7 or Windows 8 instead. As discovered in May, it’s possible to keep getting these security updates through a registry hack, but Unofficial SP4 enables this hack by default and bakes in all of its previous fixes.

More importantly, Service Pack 4 includes additional security fixes that aren’t technically part of Windows XP proper, but are instead intended for ATMs and point of sale machines still running a variant of the aging OS. Further reading: Windows XP survival guide: How to upgrade (or not)
