Windows XP Service Pack 4 Unofficial is a cumulative update rollup for Windows XP (x86) English as well as security enhancements not addressed by Microsoft. 3.1b is expected to be the final release.
It can be applied to a live Windows XP system which has SP1, at the minimum, installed or it can be slipstreamed (integrated) in any Windows XP installation media.
It includes updates for most Windows XP components, including MCE and Tablet PC. Request-only hotfixes have been included. Currently, Microsoft.NET Frameworks 4.0, 3.5, 1.1 and 1.0 (Tablet PC only) are included in the Windows XP SP4 package. Also, all post-eol updates for. NET Framework 1.1, 3.5 and 4.0 until January 2016 have been included. The .NET 1.x, 3.5 versions are automatically installed/updated in live installations. Only Microsoft.NET Framework 3.5 is enabled by default in an integrated installation. Microsoft .NET Framework 1.1 will always be installed if Media Center Edition is present.
If you download the WindowsXP-USP4-v3.1b-x86-ENU.exe you can also scan Windows Update for POSReady updates because the POSReady trick has been included.
Windows XP SP4 security enhancements: Windows XP SP4 includes registry updates to enhance security provided by Stefan Kanthak, a security expert. These security enhancements address issues not fixed by Microsoft updates.
IMPORTANT NOTICE: All SP4 users running SP4 v3.1a or earlier must delete this registry key to receive the latest WU updates:
No further action is needed. SP4 v3.1b is intended only for new installations and removes just this key.
The sp4_march16_wufix.zip file in Google Drive contains a reg file that will automate the task. Double-click on the reg file, click Yes on the popup message, and you're done! Just make sure you have administrative privileges!