OS X 10.9 Checklist

Gatekeeper was a new feature in OS X Mountain Lion and OS X Lion that builds on OS X’s existing malware checks to help protect your Mac from malware and misbehaving apps downloaded from the Internet.

Gatekeeper applies to apps downloaded from the Internet. Apps from other sources, such as file servers, external drives, or optical discs are exempt, unless the apps were originally downloaded from the Internet. Gatekeeper’s default option is to only allow you to run downloaded apps that come from the Mac App Store and identified developers.

ITS helper apps and installers are not currently signed to bypass Gatekeeper. However, there is method that you can use to open these apps. See the section titled “How to open an app from a unidentified developer and exempt it from Gatekeeper” from this Apple article for details: OS X: About Gatekeeper.