With the recent update to Windows 10, consumers no longer have the ability to permanently disable Defender, the built-in antivirus software, for any reason. However, Defender should voluntarily step down if it detects the installation of a third-party AV program (emphasis added).

Prior to the update, if users wanted to permanently disable Defender, they could edit a registry key called DisableAntiSpyware. This is no longer the case.

"DisableAntiSpyware is intended to be used by OEMs and IT pros to disable Microsoft Defender Antivirus and deploy another antivirus product during deployment. This is a legacy setting that is no longer needed as Microsoft Defender Antivirus will automatically turn off when it detects another antivirus program. Since this setting is not intended for consumer devices, we have decided to remove this registry key," Microsoft explains in its support documentation (via Windows Latest).

I am a bit torn about this decision. On the one hand, I can see the logic of not leaving consumers' Windows 10 PCs exposed to threats. After all, the web can be a dangerous place, and recently, malicious actors have attempted to spread malware through phishing emails posing as legitimate COVID-19 links.

On the other hand, however, only an experienced user could potentially dive into the registry and permanently disable Defender. Nowadays, that option is not available.

If you have a third-party AV program installed, you can only hope that Defender will be automatically disabled. Running multiple anti-virus programs at the same time may sometimes be a bad idea, as they may conflict with each other.

Nevertheless, it is easy to temporarily disable Defender. On the "Virus and Protection Settings" page, there is a switch to disable "short time before turning back on automatically" real-time protection.