A new security feature in Mountain Lion, aptly named Gatekeeper, is designed to prevent users from installing malicious or unapproved applications. By default, Gatekeeper will only allow apps from the App Store or signed under Apple’s identified developer program to be installed.
The identified developer program links apps to a digital signature, making it possible for Apple to blacklist an app and prevent it from opening across all Gatekeeper-protected machines if it is deemed unsafe. Applications signed under the identified developer program do not require any sort of approval (like they do in the App Store), but simply need to be linked with a registered dev.
If you don’t want Apple breathing down your neck every time they download a new app, it is possible to disable Gatekeeper entirely. Gatekeeper’s default settings will be helpful to average users who are susceptible to installing malware, and will keep OS X safe from potentially harmful apps.