By default, when your Windows Update done, it will request for a reboot and the annoyed prompt will prompted all the time.
Although it allow you to select remind me in 10 minutes, 1 hour and 4 hours, but sometimes when you are running a server, it is not suitable to reboot for some peak hours.
3 Options is available to disable such alert all the time.
Open the Run Command and enter cmd to enter to the command prompt.
Enter the command below and press enter.
net stop wuauserv
However this option only a temporary solution where the services might restarted again if you set it to automatically mode.
You may disable Windows Update by using Group Policies. However some version of Windows do not offer for such feature.
Go to the Run command and type gpedit.msc to enter to the Group Policies. Use the left sidebar to navigate to Computer Configuration > Administrative Templates > Windows Components > Windows Update.
Locate the No auto-restart with logged on users for scheduled automatic updates installations. Right-click the entry and select Edit from the menu. This opens a new window. Select Enable to activate the option.
Configuring it through Windows Registry. Go to Run command and type regedit and press enter. Locate to HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate\AU or create it if it is not exist.
Create a New Dword (32-bit) and name it NoAutoRebootWithLoggedOnUsers. Set the value to 1 to turn the feature on. This feature is already enabled in Windows 7 which is why Windows 7 users do not need it. Windows XP users on the other hand get an option to postpone the updates.