Windows 10: Turn On or Off Windows Defender in Windows 10  

Hi,
i wanted to turn on the defender, but i've problem turning it on, i've tried using the "reg" and "local group policy editor", but still cannot turn on, it shown below screen after i tried the method from above. please help me to turn on the defender. thanks!

Brink said:

Hello cfleong, and welcome to Ten Forums.

Do you have a 3rd party AV program installed?

If so, they will often disable Windows Defender to avoid conflicts between them.

Hi, i have uninstall the program and still find the same thing.

It was Avast, after uninstall the program and few time restart, the defender has activated itself, thanks Brink!

Thank You Sir Brink i`was using avira free AV for long time when i had XP win7 now using win10 but in this days Avira av eating a lot off ram n making slow the system. just removed Do WIN10 need 3ed party AV ?

just as add , from my tests

a.
the OPTION ONE or OPTION TWO are the same thing
just , option two can be applied silent , both reflect the same windows policy
this for pro versions

I don't know if in home versions , where on default the local group policy editor do not exist
the option two can done the job

the local group policy editor can be added in home versions
but I don't know/tested if do this job correctly.

b.
if you apply OPTION TWO
if you run somehow (Cortana,search,start....) windows defender
you will get ALSO the picture from
EXAMPLE: Windows Defender Turned Off (above)
I mean not the presented picture from OPTION TWO.8
so this mean you cannot re-start windows defender
because you will have not the red start button to press

the only way to restart windows defender after applying OPTION ONE or OPTION TWO
is to UNDO them
to undo for OPTION TWO
delete the registry value [on default the registry value do not exist and defender is on]

"DisableAntiSpyware"
from key
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows Defender
or give to this registry key the value 0 = ON
no need restart , will be instant

c.
the picture from can OPTION TWO.8 can be reached
ONLY with above policy enabled
and service windefend not started [no running]
for that you must change the registry value

HKLM \SYSTEM\CurrentControlSet\services\WinDefend
valuename "Start" to 4

Automatic = 2 , Manual = 3 , Disabled = 4 , Automatic (Delayed Start) = 5

but this registry key is protected and windows don't let you change

but anyway is doable , for do that you must
-apply OPTION TWO (set off policy = unprotect the start key)
-restart
this if not already done before
-change start to 4 (service windefend will not start next boot)
-restart
-undo setting OPTION TWO (set on policy, but windefend service will remain stopped from now)
nou you will have access to the presented picture in OPTION TWO.8

OR change the start value with a program/script based on RunAsTI ( run as trusted installer)
like I do

OR maybe take ownership can do the job for start value in registry
not tested , and I don't have such intention , because i am not a fan of this way
[can be dangerous in future , in my opinion , malware can use this kind of door(s)]

d.
sorry if is so complicated my add
you can just use OPTION TWO for disable/enable the policy and is ok

c