Ok, maybe with OSX Mountain Lion you have some problems during the installation of a cracked program or maybe with a small app that one of your friends developed. It says something like “can’t be opened because it is from an unidentified developer”; here’s the screenshot:
You can’t install them because of the new security programs in Mountain Lion but you can disable this to enable the installation of one app.
First go to System Preferences and click on Security.
Once inside Security click on general. Select Anywhere and you are done.
We recommend activating this after you install that trusted app, just to be sure that nothing unwanted is installed.