Here's the skinny.

I turned a computer into a guinea pig.

For 20 months I used only a firewall, opera and firefox.

The browsers were stock and kept up to date.

The computer OS was not updated.

After the 20 months I scanned the whole computer with

updated windows defender and found nothing.

The computer works great, don't try this at home.

Services

Background Intelligent Transfer Service

Delivery Optimization

Update Orchestrator Service

Windows Update

All are disabled

The last 2 must be on to access recovery.

Kill windows defender updates

Administrative tools 

run as administrator

Windows Firewall with Advanced Security

Block incoming and out going MpCmdRun.exe (Microsoft Malware Protection Command Line Utility)

it is in windows defender program folder.

Kill auto installing apps

Block app installer in firewall and or uninstall in apps.

Turn off auto update by the computer manufacturer. Hunt it down they are all different.

You are on your own with your programs.

I trust no security software all I have used screwed the start sequence

and I had to get rid of them before the computer was inoperable.

You can trust them if you like to. I have had no problem with windows defender yet.

Use opera and firefox preferably at the same time.

Don't try this at home.

The following works on windows 8.1

Cut down on unnecessary auto maintenance.

Set windows defender to custom scan and don't select any thing.

It still scans processes or something.

It will reset to quick scan after restart.

I do a quick scan once a week with the other maintenance.

Why scan it if nothing changes I have real time scanning on.

Speed up your computer,turn off real time scanning.