A voter-profiling company used by the 2016 Trump campaign collected the private data of over 50 million Facebook users without their permission—one of the biggest data leaks in Facebook history, the New York Times reports. According to the Guardian, it started with researchers concluding they could form complex personality profiles of people by what they "like" on Facebook, determining intelligence, history of trauma, and more based on responses to posts on innocuous subjects like curly fries and Hello Kitty. Researcher Aleksandr Kogan signed a deal with Cambridge Analytica—which had Stephen Bannon in a leading role—and in 2014 developed a personality quiz that would not only harvest the data of the Facebook users who took it but also all of their friends.
Around 270,000 Facebook users took the quiz—agreeing to allow their data to be used for academic purposes; their friends didn't even agree to that—which allowed Kogan to harvest the data of over 50 million Facebook users and pass it along to Cambridge Analytica in violation of Facebook policies. The company used it to create psychographic profiles of about 30 million US voters and target political ads toward them. Facebook found out in 2015 and demanded the data be deleted, Quartz reports. But Facebook didn't publicly acknowledge the leak until Friday and, despite claims to the contrary, it appears Cambridge Analyitica still has a good portion of the data. Cambridge Analytica, which has now been banned by Facebook, is also facing the possibility of having run afoul of US election laws and is being looked into by the Mueller investigation.