Apple took a stance against unsigned applications from third-parties by enabling Gatekeepter in Mountain Lion, which only allows users to download apps via the Mac App Store or verified developers. Fortunately, there's a setting tweak that'll let you change this.
By default, if you load up an application downloaded from a third-party that isn’t verified by Apple, then you’ll get the error message that the application “Can’t be opened because it was not downloaded from the Mac App Store.”
You can get around this by tweaking the Gatekeeper settings located in System Preferences > Security & Privacy > General.
If you are not authenticated as an administrator, you may need to click the lock at the bottom of the preference pane to authenticate before making any changes.
From here, you have three options: Allow from Mac App Store, Mac App Store and identified developers, or Anywhere.
Selecting “Mac App Store” means that your Mac can only run applications downloaded and installed from the Mac App Store.
Selecting “Mac App Store and identified developers” will let you install both applications downloaded from the Mac App Store, and third-party signed apps downloaded from developers’ websites.
By selecting “Anywhere,” your Mac will behave just as it did before you installed Mountain Lion. With this option selected, you will be able to install any application, regardless of its origin. This setting should only be used if you are downloading third-party applications unsigned, but from a trusted developer. As a precaution, you should never install applications that are from untrusted developers.
Cory Bohon is a freelance technology writer, indie Mac and iOS developer, and amateur photographer. Follow this article's author, Cory Bohon on Twitter.
demonsmooth
July 27, 2012 at 10:07am
Since installing Mountain Lion there are so far 4 Apps I can't open, Reminders, Contacts, iPhoto and when clicking Security and Privacy nothing happens. :-(
The Mac OS releases are incrementally getting worse. Too bad, because I like my MacBook Pro. Use to love it with Leopard. Leopard never crashed on me or my wife.
b9bot1
July 30, 2012 at 9:15am
It sounds like you need to visit the Apple Store with a Genius Appointment. If you don't have one near by, try Applecare. When an install goes bad, there could be many factors involved. Errors already on your hard drive,
corrupted software, software that was not up to date. Some things you could try to resolve your issues is to run Disk Utility located in the Utilities folder. You can easily get there by going into finder and then at the top menu click on the go menu and scroll down to Utilities. Select Disk Utilities then once booted select Macintosh HD and do a verify on your drive.
If there are errors make sure you have your data backed up FIRST before you do anything else.
Then you can proceed and restart your computer and then hold the option key down. This will bring up the boot loader which will give you access to the hidden recovery partition. Select the language then select Disk Utility again. Remember you need to back up first. If you have backed up then you can again select Macintosh HD and click on the repair button. If the repair is successful you will be notified with green text. If not it will show red text which means your hard drive is either bad or the volume Macintosh HD is corrupted and you will need to do an erase and install. This is why I stress the backup part so much.
Call applecare and they can walk you through that process.
