- Verify Gatekeeper is still turned on
- Go to System Settings
- Security and Privacy
- Verify Gatekeeper is set to Mac App Store and identified developers
- Be sure to not install apps from unidentified sources
- You will be presented with a dialog like the one below asking if you are sure you want to install an application from an unidentified developer.
- If you DO NOT know this developer and trust the application you are installing, hit Cancel. When it doubt, live without the application.