You are trying to install or open an app that didn't come from the Mac App Store but you got a message saying App can't be opened because it is from an unidentified developer. This is how you bypass it.
Mac OS X 10.8 Mountain Lion is out and ready for download. If you are willing to invest $20 and an hour of your time to upgrade you Mac computer, you won't be sorry.
Mac OS X Mountain Lion has 43 secret desktop wallpapers hidden in one of its folders. They are all beautiful, high quality and this is how you find them.