Another advantage of the Mac App Store, besides pausing downloads, safe uninstalls, and easy re-downloads of Mac OS X apps, is the safety of knowing that anything in the Mac App Store has been vetted by Apple.
One way your Mac makes sure you’re (relatively safe) from rogue apps is what’s called Gatekeeper. By default, this bit of software only allows you to install verified apps from the Mac App Store on your Mac. What if, however, you want to download software from a Mac developer who doesn’t distribute their software on the Mac App Store? You’ll need to bypass Gatekeeper in order to do so.
Here’s how to do that safely.
Launch your System Preferences app and head to the Security & Privacy preference pane. You have three choices here. You can set Gatekeeper to Allow applications downloaded from the Mac App Store, the Mac App Store and identified developers, or Anywhere. The safest of these options is obviously the first one, as it will keep any software not downloaded via the Mac App Store from running on your Mac.
Keep either of the top two options enabled, and when you download any app that isn’t from the Mac App Store, nor from an identified developer, your Mac won’t let you run it.
If you want to bypass this security feature, find the offending app, and right click on it. That’s a two-finger click on a Macbook trackpad, a Control-click on a single button mouse, or the actual right mouse button on a multi-button mouse.
Choose Open in the pop up menu, and then choose Open on the resulting dialog box, which will tell you that the app you’re trying to open is from an unidentified developer. Once you choose to Open it this way, the app will no longer trigger a Gatekeeper warning, so be sure you know and trust the developer you got the app from.