Type in Defender into the search bar, and click on the Defender program in the list. When Windows Defender opens, click Settings and turn off real time protection. I just noticed that it will reenable it automatically after some time, geez.
I suppose you will could install some third-party antivirus software that does not flag hack tools and such as a threat. There is a third-party application called NoDefender to disable it permanently, but I have not tried it or can vouch for it or what it actually does to accomplish this. I found this note on another website, but I am not sure if it is true or not. Better make a restore point anyway.
NOTE: The NoDefender utility doesn’t include an option to enable Windows Defender again. So we suggest you create a manual system restore point before disabling Defender if you want to easily enable Windows Defender again in the future.
Another method is to rename the Defender program folder. This must be done from a Linux Live DVD or USB: C:\Program Files\Windows Defender.
Another method is to disable the Defender Service from starting in the Windows registry as it cannot be done from Services directly as options are grayed out.
Open regedit and go to
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\WinDefend
Open the subkey corresponding to the service you wish to change (WinDefend), and modify the value of 'Start' to equal either "2" (for automatic), "3" (for manual), or "4" (for disabled).
(Registry edits have the advantage for Windows Home or lower versions, as they do not have Group Policy Editor to do it as suggested by Nate's answer.)
Alternative solution if this does not work for you
Found the answer myself (more details here). Basically, it's as simple as setting the Group Policy called Monitor file and program activity on your computer to Disabled.
For users of Windows editions without gpedit.msc, a DWORD entry called DisableOnAccessProtection must be created under HKEY_LOCAL_MACHINE\Software\Microsoft\Windows Defender\Real-Time Protection and set to 1.
The name of this registry entry tells you exactly what "Monitor file and program activity" actually do: It scans files "On Access" (such as when Windows Explorer lists the contents of a directory). Nothing more.
Best Answer
I have successfully removed the windows defender service with no side effects so far, other than windows notifying you that the defender service could not start.
Windows 10 Version 2004 build 19041.450
This eliminated defender from the PC
Use a bootable offline registry editor of choice, I used a windows 7 64bit ERD disc to do it, not publicly available but can be found. It has a registry editor.
Once booted into the registry editor navigate to
delete the WinDefend key
I would export the key first, then if you want Defender back you can Merge the saved key back into the registry and reboot.
The key may be returned after certain Windows updates, so you will have to delete it again, thanks IGRACH