If you are running Mountain Lion, you may have come across the following message when trying to install new software:
[Program Name] can’t be opened because it is from an unidentified developer.
This is Mountain Lion’s new feature, Gatekeeper. What it does, is only allows you to install software from the Mac App Store or from developers who are known and registered with Apple. While you can turn off the Gatekeeper feature, it is not recommended as it can prevent rogue software from being installed without your permission.
So how do you install software from developers who may not yet be registered with Apple? All you need to do is right-click or Control-click the software’s icon and choose Open from the contextual menu. You will be asked if you really want to install software from an unidentified developer. Once you do this the first time, the application will run without any security warning messages in the future — opening it once permanently “clears it” with Gatekeeper.