Windows 2012 prevent reboot
Our office Windows 2012 server insists on rebooting during office hours showing us a screen shot like this:
To prevent the reboot simply disable the update service using the following command which you must run as an administrator through the command prompt or powershell:
net stop wuauserv
Remember though that if you log out and log back in the service will kick-start again and you'll need to re-apply the command.