Investigations published in London and New York revealed that data on tens of millions of Facebook users had been obtained through a personality quiz application and passed to Cambridge Analytica, a political consultancy.
The app collected information not only from people who installed it but from their friends, under platform permissions in force at the time. Facebook's share price fell sharply and Mark Zuckerberg was called to testify before the United States Congress and the European Parliament.
The episode accelerated privacy regulation worldwide and coincided with the entry into force of the European Union's General Data Protection Regulation.
