Running Norton Security with Backup 22.0.2.17 on Windows 8.1 x64.
Normally Norton disables Windows Defender (see this picture). But lately I noticed that Windows was complaining about failed updates. Looking at the update history, it still tried to install Windows Defender definitions.
Opening Defender does not give the message in the linked picture above, but this instead:
I'm unable to disable Defender myself, because I keep getting Access Denied errors.