Gatekeeper Security

Mountain Lion can monitor the origins of applications you add to your machine and warn you if they might not be what you prefer. This feature is known as Gatekeeper. With Gatekeeper, you can choose to run only apps from the App store written by developers registered by Apple, allow App store apps by unregistered developers, or allow any apps from any source to run. Depending on how Gatekeeper is configured, you'll see various alerts about the security of apps you add to your machine.

1. Go to the Apple menu and choose System Preferences.
2. Click the Security & Privacy icon.
3. Click the General tab.

The Gatekeeper section at the bottom of the dialog helps to control what happens when you try to download new applications. These options control warning messages that you'll see when you try to install something that this choice doesn't allow.

• If you choose the Mac App Store option, apps that you didn't download from the App Store will not be allowed to run when you try to launch them.
• The safest option is Mac App Store and Identified Developers, which limits your new programs to App Store apps created by Apple identified developers. This means that the app has been submitted by a developer that registered with Apple and received a personalized digital certificate they can use to sign their apps cryptographically. Signed apps can be checked to see who developed them and if any modification has occurred since the developer submitted the app to the App Store.
• The riskiest option is Anywhere. Choose this option and you'll instantly see a strongly worded warning message. This option lets you install anything you want that isn't yet known to be malicious software.

Excerpted from OS X Mountain Lion: Peachpit Learning Series by Lynn Beighley