Facebook employees were aware of concerns about“improper data-gathering practices” by Cambridge Analytica months before the Guardian first reported, in December 2015, that the political consultancy had obtained data on millions from an academic. The concerns appeared in a court filing by the attorney general for Washington DC and were subsequently confirmed by Facebook.

https://www.theguardian.com/uk-news/2019/mar/21/facebook-knew-of-cambridge-analytica-data-misuse-earlier-than-reported-court-filing