Why?

It’s annoying if Windows keep updating automatically in the background and even reboot when idle.

Risk?

Yes, If auto updates are disabled, one should take care to manually update Windows on a regular basis.

How?

Run PowerShell (as Administrator):

function disableWindowsAutoUpdate{
    param(
    $windowsRegHive='REGISTRY::HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows',
    $hiveName='WindowsUpdate',
    $keyName='AU',
    $disable='0'
    )
    try{
        # set the Windows Update service to "disabled"
        stop-service wuauserv -force
        set-service wuauserv -startup disabled
        $currentAUSettings=(get-itemproperty 'REGISTRY::HKLM\SYSTEM\CurrentControlSet\Services\wuauserv').Start
        if($currentAUSettings -eq 4){
            write-host "Windows Automatic Updates have been disabled."
        }        
        $autoUpdateSettings = (New-Object -com 'Microsoft.Update.AutoUpdate').Settings
        $autoUpdateSettings.NotificationLevel=1
        $autoUpdateSettings.Save
        write-host "Option to 'never check for update (not recommended)' has been set"
        
        # Set Windows AU registry key
        if(!(get-item "$windowsRegHive\$hiveName")){
            New-Item -Path $windowsRegHive -Name $hiveName -Force
        }        
        $null=New-ItemProperty -Path "$windowsRegHive\$hiveName" -Name $keyName -Value $disable -PropertyType DWORD -Force
        write-host "Registry key $keyName has been set to value $disable"
        return $true
    }catch{
        write-warning $_
        return $false
    }
}
# Legacy commands
REG ADD HKLM\SYSTEM\CurrentControlSet\Services\WaasMedicSvc /v Start /f /t REG_DWORD /d 4
REG ADD HKLM\SYSTEM\CurrentControlSet\Services\wuauserv /v Start /f /t REG_DWORD /d 4
REG ADD HKLM\SYSTEM\CurrentControlSet\Services\UsoSvc /v Start /f /t REG_DWORD /d 4