Apple changed the rules for obtaining digital signatures for applications in OS X

Installing programs not from Mac App Store - it's one of the few ways to get on my poppy malicious software.

 So Apple has long used in OS X function Gatekeeper, which blocks the running of applications from unknown developer. Moreover, in the next update of OS X Mavericks and the final version of OS X Yosemite will change the rules, which are oriented software developers to obtain a digital signature from Apple and the possibility for the application to be installed on users' computers. For users, this means a few more annoying messages about potentially dangerous software. 

In fact, changes to Apple, is not as serious as it may seem at first glance. Now, to sign your application developers should use OS X 10.9 or newer operating system. And if the application in the Mac App Store from virtually not affected because it is a standard procedure prior to publication, the developers who extend their programs outside the app store will need to re-obtain a digital signature using OS X Mavericks. Otherwise, the Gatekeeper will block the launch of the program. 

It is expected that in this way Apple is trying to improve the compatibility of the software with the latest version of its operating system, while running the program with the updated signature will be on the older versions of OS X. However, users will still be able to bypass the warning Gatekeeper, run the program from the context menu in the Finder. Therefore, the only category of users who are really affected by the new rules - it's the developers who have not yet upgraded to OS X Mavericks.