"Somebody at Microsoft should have tested the patch before releasing it, but fortunately there's an easy fix" ...
There's one little problem with this patch: It looks like Microsoft didn't test it on Windows 10 systems. Judging by the hue and cry, I would guess that at least a third of the people trying to install KB 3087040 on their RTM Windows 10 systems (build 10240) are getting this message:
There were problems installing some updates, but we'll try again later. If you keep seeing this and want to search the web or contact support for information, this may help:
Security Update for Internet Explorer Flash Player for Windows 10 for x64-based Systems (KB3087040) - Error 0x80004005