I first caught wind of this project a few months ago, but then reminded about it through an article posted by Toby Wolpe on ZDNet today. When I first learned about it, I decided not to write about it with the intention not to draw attention to something that is a) unsupported, and b) not a good idea.
In September 2013, an individual going by the name of harkaz and located in Greece decided to ramp up interest in a project to pull together known updates for Windows XP and start to build an unofficial Service Pack 4. Windows XP, as you know, reached end of life in April 2014 and is no longer supported by Microsoft. Obviously and according to recent stats, there are many still running the expired operating system version. There are many reasons why Windows XP is still being used. In a small number of cases, like manufacturing, it's warranted and those that must continue to use it should seek extended, paid support from Microsoft while working to eliminate it.
Over the course of the project, harkaz has chosen and collected updates from Microsoft's Download site and then infused other updates by request of forum posters and followers. A release candidate is being finalized and is expected shortly. Harkaz's SP4 requires at least Windows XP SP1 and works for x86 systems. He also states that SP4 includes updates for most components, including MCE and Tablet PC. And, of course, Softpedia is making the unofficial SP4 available for download. SP4 weighs in at a hefty 827 MB.
My take? Avoid it at all costs.
It doesn't matter if harkaz's SP4 includes every known update for Windows XP ever, applying it does not make Windows XP any safer. Windows XP is outdated and comes nowhere close to meeting security protection and standards of today's world. Windows XP is 12 years old, meaning that a lot has changed since the OS released. Applying SP4 is like installing an air freshener in a downhill car with a snapped brake line and no seat belt.
P.S. No links were provided in this commentary on purpose.