How to Allow app installation from unidentified developers on Mac

When being unable to install the HMA! Pro VPN client for Mac or other software, you might see the message "This app can't be opened because it is from an unidentified developer" You can easily fix this by navigating to: System Preferences > Security & Privacy In the "General" tab, click the little lock icon in the bottom left of the window to unlock making changes. Now select "Anywhere" under "Allow applications downloaded from:" Now try to install the software again.