From The Guardian: By late 2015, Facebook “had found out that information had been harvested on an unprecedented scale. However, at the time it failed to alert users and took only limited steps to recover and secure the private information of more than 50 million individuals.”
UPDATE:
Senator Klobuchar tweets:
“Facebook breach: This is a major breach that must be investigated. It’s clear these platforms can’t police themselves. I’ve called for more transparency & accountability for online political ads. They say ‘trust us.’ Mark Zuckerberg needs to testify before Senate Judiciary.”