Gatekeeper

Gatekeeper is a security feature of the macOS operating system that enforces code signing and verifies downloaded applications before allowing them to run, thereby reducing the likelihood of inadvertently executing malware. Installing software applications on Mac is easy when using the Apple App Store. Installing software applications from other sources is never easy and will be blocked when you try to install from a downloaded installer file. They are blocked by a specific security feature which is called Gatekeeper.

System Extension Blocked

By default, when macOS is installed, Gatekeeper is set to allow software from the App Store only.

To Bypass

In the security & privacy panel of System Preferences, the user has three options:

• Mac App Store - Allows only applications downloaded from the Mac App Store to be launched.
• Mac App Store and identified developers - Allows applications downloaded from the Mac App Store and applications signed by certified Apple developers to be launched. This is the default setting since Mountain Lion.
• Anywhere - Allows all applications to be launched. This effectively turns Gatekeeper off. This is the default setting in Lion. Since macOS Sierra, this option is hidden by default.

Another option

You can bypass Gatekeeper restrictions by control-clicking the application and selecting Open from the pop-up menu. A new alert warns you the software is unverified by Apple and may contain malicious software, but you can still choose to Open it anyway.