Apple set up Gatekeeper as one of the prime methods to protect users from malicious software. It's basically a security system integrated into macOS which checks executable software against a list of malicious stuff.I recently noticed that in Apple's latest desktop OS "Mavericks" (10.9) there is no Gatekeeper setting for allowing any kind of software to run on your Mac. You can find Gatekeeper settings in the "Preference" App under option "Security" in the "General"-Tab. There you are now limited to allow App-Downloads (just) from the Apple App Store; or from the Apple App Store and from verified Developers.Previously there was a setting for 'allow from - "Anywhere" '. This was useful to me in certain situations - basically during troubleshooting certain Apps.Here is how you get this "Anywhere" Option back under Mavericks:Open Terminal and enter this command (confirm with Admin Password):

sudo spctl --master-disable

And that's it. The formerly available Option returns to your "Preferences" App.