There are reports this morning about a new patch, KB 3150513, appearing on Windows 8.1 systems -- and probably lurking on Windows 10 systems, too.
Fortunately, poster PeterBisco on the Microsoft Answers forum, has an explanation (originally posted on the Polish forum):
I have made a look into Windows8.1 version of this update and found this:
This update doesn't contain binary code. It just contains new data for AppRaiser (Windows 10 Compatibility tool). It contains files as:
So if you want to upgrade to Windows 10, and you have all the Windows 10 related updates installed (e.g. KB3035583, KB2952664, etc.) then you are safe to install this patch. If you don't want Windows 10 or its related updates and you have hide them, you can hide this one as well, if you wish.
AppRaiser is the Windows 10 compatibility appraiser, which you can download and run manually. It's the program that's supposed to tell you if you're running any software or have any hardware that will mess with the Windows 10 upgrade.
Hiding this patch sounds like good advice to me.