OSX Mountain Lion: How To Disable Gatekeeper
Gatekeeper is a new feature in Mountain Lion that builds on OS X's existing malware checks to help protect your Mac from malware and misbehaving apps downloaded from the Internet.
Although having Gatekeeper enabled keeps you safe, it will not allow you to install some third party applications. If you want to install open source software or third party applications you will need to disable Gatekeeper.
OSX Mountain Lion
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