Service Pack 3 of MS Windows XP went out last April 29, but it wasn’t final yet. It was only available in the Windows Download site.
Today, WinXP SP3 is finally available via the Windows Update. You should be getting alerts by now if you have Automatic Updates enabled on your Windows PCs.
The final build of SP3 (5512) reportedly includes 1,073 fixes, including every security update, out-of-band release, and hotfix released last August 2004.