If you are a third-party app developer for Mac devices, then you had best get your act together since a recent change in the latest OS X Mavericks and Yosemite developer versions. The reason is because Gatekeeper has made a change, which means devs will have to re-sign their applications and then submit their updates to the Mac App Store.
If they do not do these, then the app will show up as not having a valid signature, meaning there will be an incompatibility with your app on both Mavericks and Yosemite.
This is not an issue for version of Mavericks older than 10.8, but will be a problem for users running newer versions of the Mac operating system. The worst hit with this problem are the app that are downloaded from other sources rather than the Mac App Store, and so they will now be forced to comply with the new standard.
There is a way to work around this issue – These third-party app developers will now be working hard to make certain they update their apps with new signatures. However 9to5 Mac reports that if you come across an app that is unable to run because of this change can right-click on the app and then select Open, this will bypass Gatekeeper. You will need to do this for each app that no longer runs.
However, app developers are still asked to go along with this change and make the necessary update, as there will be less risk of potential issues once Yosemite gets it public release, something we are certain users of these apps will agree with.
Also See: iOS 9 OTA beta 3 update notes live