If you see following alert when trying to run an app: “App” can’t be opened because it is from an unidentified developer. It means that Mac OS X is forcing you to run only Apple approved software by default. Of course you can change the options, which will allow you to install any application you want.
Apple uses this alert to provide security to it’s system. For example Android devices also uses this type of security which alerts you and blocks installation of apps from unknown developers, and you can change this option to permit you the installation.
How It Works
When you launch a fresh installed application on your Mac, the system checks to see that the developer of this application is signed with a valid signature. If it doesn’t you will be alerted with a warning message by default. This warning alert has many security reasons, it can contain viruses, or it can be a different app than the one the title and icon seems to be. If the application will have a valid signature the system will allow you to run it, if the application will not have the valid signature it will be blocked with the following warning alert: “App” can’t be opened because it is from an unidentified developer
This setting is controlled from the System Preferences window. Click the Apple menu, select System Preferences, and click Security & Privacy. On the General pane, click the lock and enter your password. You can then modify the setting under “Allow apps downloaded from.”
How to Change the Setting
To change the setting to permit you to run any app you want, you will have to go to System Preferences by clicking the Apple menu and selecting System Preferences, then click Security & Privacy. On the general tab click the lock and enter your password, now you will be able to modify the setting under “Allow apps downloaded from:“.
You can choose the system to permit you to run apps from “Mac Apps Store” only, or from “Mac App Store and identified developers” or from “Anywhere” which means the developers will not be checked for a valid signature.
Installing an Unsigned App
If you will download an unsigned application, you’ll see the alert. The app will be blocked from running, of course you can change the settings to allow you to run it. Pay attention this alert is for security reasons, as you can accidentally downloaded a malicious app, and running it will have bad consequences. By default Apple will allow the system to run only trusted, verified and signed developers.