Apple's next major operating system update for Macs will, by default, block users from running games and applications not downloaded from the Mac App Store or created by a developer registered with the company.



A new feature in the update called Gatekeeper automatically prevents users from running games that are from unregistered developers and that they've downloaded from the web -- similar to how iPhone or iPad owners can't install apps that don't originate from the App Store.



Users can choose to remove that restriction, increase security by allowing only Mac App Store programs to run, or load an app anyway by right-clicking on it and hitting open, but when they first install Mountain Lion, Gatekeeper will refuse uncertified, non-Mac App Store titles by default.



This feature is meant to increase security and combat malware from taking root on users' computers, as its reviewers inspect each Mac App Store submission before approving it for release, and the company can remove problem software from the shop.



Developers who don't want to register with Apple but still release apps and games through other channels, such as their own websites, might not appreciate this restriction and the slightly heightened barrier of entry it creates for users to install their titles.



If they want to avoid those issues, though, they will need to sign up for Apple's Developer ID program, which gives developers a unique ID for signing their apps. The ID is designed to verify whether their app is known malware or has been tampered with. If a developer is found to be distributing malware, Apple could revoke their certification and prevent users from loading any of that developer's apps.



The OS X Mountain Lion update is meant to further unify the offerings of Apple's iOS and PC operating systems, creating a consistent experience. Along with Gatekeeper and other new features, Apple will carry over its iOS social network Game Center to Macs. This move should greatly increase Game Center's audience, which already has over 100 registered million users across iPhones, iPod Touches, and iPads.



By bringing the mobile game social network to Macs, Apple will enable developers to release titles that support cross-platform multiplayer. Someone with a Mac copy of a game could play against another person with an iOS version of the title.



Game Center for Mac will also allow developers to tap into online and community features like leaderboards, achievements, friend requests, voice chat, and more. The network allows users to see what their friends are playing and discover new games, too.



Apple says more than 20,000 games on iOS's App Store use Game Center -- plenty of titles also use third-party social networks like Gee's OpenFeint and Gameloft Live, which support cross-platform play across iOS and Android devices but not Macs.



OS X Mountain Lion is expected to release this summer through the Mac App Store as a paid product, not a free system update.