Someone at Apple just forgot to renew a digital one certificate, causing the entire Mac App Store to go offline operation, or to put it better, started distributing applications to thousands of users that were impossible to install. 
Software manufacturers use digital certificates for verification ID cardς της πηγής της εφαρμογής. Χρησιμοποιούνται κυρίως για λόγους security, allowing operating systems to recognize that an application about to be installed on the system comes from a trusted source.
But to avoid any cheating, companies use digital certificates that only apply for a few months or years.
This is exactly what happened on November 11, 2015, when the Apple Digital Certificate, which is automatically added to every App Store app, just expired.
So users who downloaded applications from the App Store after the expiration date acquired applications that could not install them on their computers.
An indie developer spotted the issue, posted it on Twitter, and of course someone from Apple fixed it problem issuing a new digital certificate for the App Store.
Meanwhile, Apple continues to be one of the top companies in the stock market, and it is hard to imagine how such issues are.
If you downloaded an app in the last few days and you are experiencing installation problems, you can simply download it again.
https://twitter.com/tapbot_paul/status/664653066679906304
