https://www.techradar.com/news/were-you-hit-by-cambridge-analytica-facebook-will-be-letting-you-know

Facebook users may about to see the first informative post in a long time at the top of their News Feeds today as Facebook has announced that it will be sending alerts to those affected by the Cambridge Analytica data scandal. 

Facebook has estimated that around 87 million users had their personal information harvested and used by Cambridge Analytica. The majority of the users affected are believed to be based in the US (around 70 million) with another million users in the UK, Indonesia and the Philippines.