You can simply uninstall KB 3004394 as it is not an essential update - after that Windows Update does work again (but restart your PC first) and you have to restart Windows Defender from the System Menu as well (i had to unchec/check the Checkbox in the "Extras" Settings of the Windows Defender to make it start with the PC.
PS:
http://www.infoworld...il-defende.html
Edited by Thorqemada, 11 December 2014 - 04:23 AM.