Privacy concerns have swamped Facebook since it acknowledged last month that information about millions of users wrongly ended up in the hands of political consultancy Cambridge Analytica, a firm that has counted U.S. President Donald Trump’s 2016 electoral campaign among its clients.

Zuckerberg said on Wednesday under questioning by U.S. Representative Ben Luján that, for security reasons, Facebook also collects “data of people who have not signed up for Facebook.”

Lawmakers and privacy advocates have immediately protested the practice, with many saying Facebook needed to develop a way for non-users to find out what the company knows about them.There si a massive uproar among privacy advocate who call this move unethical.