I don't know how many folks signed up for Robinhood via SA (I started but stopped when they asked for SSN) but there is now a class action because of the recent data breach. The Robinhood Stolen Data Class Action Lawsuit is Zullo, et al. v. Robinhood Markets, Inc., Case No. 1:21-cv-06253, in the U.S. District Court for the Eastern District of New York. You'll have to google search to find out how to join.