Facebook says it discovered a security breach affecting nearly 50 million accounts The company says hackers exploited the "View As" feature It lets you see what your profile looks like to someone else Facebook says it has taken steps to fix the security problem and alerted law enforcement Facebook says 90 million people will have to log in again Facebook says it doesn't know who's behind the attacks or where they're based It's the latest security problem for Facebook The world's leading social media site has dealt with agents from other countries posting fake political ads since 2016 This year, Trump-linked data analytics firm Cambridge Analytica gained access to data from millions of users