I have updates that are launched. Everything is set to not reboot the machine but there was already a machine that did a reboot at 3.15AM.
The log in event viewer is
The process C:\Windows\system32\svchost.exe (X656REZ) has initiated the restart of computer X656REZ on behalf of user NT AUTHORITY\SYSTEM for the following reason: Operating System: Recovery (Planned)
Reason Code: 0x80020002
Shutdown Type: restart
Comment:
It indicates that something from SCCM, as it's using the SYSTEM account, triggered that reboot. It appears that when updates are deployed from SCCM, the WU client will itself do a reboot as the SCCM agent won't.
In group policy you can disable this by going to
Choose the 'No auto-restart for scheduled Automatic Updates installations' and set it to 'enable'.
If you have seen this, apply this 
Also the updates are by default set to check for updates at 3AM
You can also disable this with the GP 'Configure Automatic Updates' but I don't know if this will resolve my problem too?
This page explains how you can have the full control over windows update: http://www.solvusoft.com/blog/should-you-turn-off-automatic-updates-in-windows-7-and-how-to-do-it/
