Aleksandr Kogan collected direct messages sent to and from Facebook users who installed his This Is Your Digital Life app, the Guardian can reveal. It follows Facebook’s admission that the company “may” have handed over the direct messages of some users to the Cambridge Analytica contractor without their express permission. The revelation is the most severe breach of privacy yet in the Cambridge Analytica scandal.
Source: Revealed: Aleksandr Kogan collected Facebook users’ direct messages | News | The Guardian
Note – other apps had the ability to do this too. This is not just limited to Kogan’s app and Cambridge Analytica.
Having just finished reading Code Warriers by Stephen Budiansky, it seems 100% likely that US spy agencies would have used these methods to collect everything as well (at least for all FB users outside the U.S.).