The latest version of Mac OS X (Mountain Lion) has Gatekeeper enabled by default. Gatekeeper is a system designed to restrict which sources users can install applications from, in order to reduce the chance of inadvertently executing applications containing trojan horses, virus and malware. The default settings will prevent running applications that have not been downloaded from the Apple app store or digitally signed by a developer. If you download an unsigned installer, you will be greeted by a pop-up similar to the below and will be unable to install it unless you modify the system-wide settings
let us know if you run into any issues. While we are at it, we have decided to add digital signatures to the Windows downloadable installers and will be rolling those out in the near future.