I have Vista os w/ service packs 1 & 2 and all updates (except Bing toolbar install), with Firefox 27.0.1, on an older Gateway laptop, from maybe 2006/7.
I just tried to install this update minutes ago along with an Essentials definition update that accompanied it and my computer crashed, screen went black suddenly, eventually taking me to the windows startup error screen, and I chose the start windows normally option and hit the enter button on my keyboard.
Upon rebooting, my icon was green, but I found the two updates waiting to be installed again. The installation was therefore rejected, no explanatory popup as to why. I have never had such a response to a MS update before, never.
Something is very wrong with this update. I will hide it, but if it keeps coming back, I will have to give up Security Essentials and use another product. Scary.