Apple has built a 'Gatekeeper' to help protect Mac OS X users from downloading and running malicious software.
The new anti-malware feature, now fitted into the new OSX Mountain Lion, works behind the scenes to let Mac users either allow or deny application downloads based on where they come from.
In the "Security and Privacy" preference, the end user gets the choice over whether to allow applications downloaded from:
Mac App Store
Mac App Store and identified developers
The pre-checked default is the "Mac App Store and identified" developers, a setting that works in tandem with Apple's new Developer ID Program.
As part of the Mac Developer Program, Apple gives developers a unique Developer ID for signing their apps. A developer’s digital signature allows Gatekeeper to verify that their app is not known malware and that it hasn’t been tampered with. If an app doesn’t have a Developer ID associated with it, Gatekeeper can let you know before you install it.