If you have Windows 10 installed and also have an NVIDIA graphic card you might run into a problem installing KB3074683 where the computer restarts several times and fails to install the "Security Update for Windows 10 for x64-based Systems (KB3074683)".
Have you been trapped in a reboot loop? The update reaches a certain percentage of installation before failing and rolling back.
This might be a solution to the endless reboot cycle. It worked for me.
Run regedit in Windows. Hold down the Windows button on the keyboard and press R and enter regedit and click on OK. (As always with regedit, be careful and if needed make a backup of the registry first)
Then locate this key:
Now right click on ProfileList and select Find and enter UpdatusUser and click Find Next.
On the key where you find UpdatusUser in the ProfileImagePath, right click and click on Delete.
Now let Windows 10 make the update and hopefully it works for you too.