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On Windows version 1803 after April updates installation (KB4493464) computer systems starts reporting that two antivirus software are active. TeamViewer Endpoint protection and Windows defender.
You can deactivate the built-in antivirus software in Control Panel (Settings).
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Is this situation still happening? When we tested the release candidate for the April release everything was working as intended and the call to turn off Windows Defender worked. After the April release re got a few reports like this, however, we could not find the cause as it is not a reproducible scenario and it does not affect many systems. From what we found is that after the next reboot the call to disable Windows Defender works.
If the situation is still the same and manual action is needed to disable Windows defender please reach out to our support to investigate this situation further.