June 22, 2012, 6:17 PM — Here's how you can change the Gatekeeper settings in OS X Mountain Lion. Gatekeeper is Apple's new security tool to help protect your Mac from viruses and malware.
1. Go to System Preferences.
2. Click the Security & Privacy icon.
3. Go to the General tab.
4. Click the lock in the bottom left corner to make changes.
5. Type in your password then click the Unlock button.
6. You have the following options under "Allow applications downloaded from:"
Mac App Store
Mac App Store and identified developers
7. Just click the button next to whichever option you want to use in Gatekeeper.
Gatekeeper defaults to the "Mac App Store and identified developers" option. But you can change it easily to whatever you want.