This crisis is Facebook's largest to date, the Cambridge Analytica data breach and subsequent fallout. Initially Facebook threatened legal action to keep the press from reporting this story; when that failed Facebook announced it had suspended Cambridge Analytica (the day before the story was published). Once the story came out, Facebook stock plunged losing more than $35 billion in market value.
Whistleblower Christopher Wylie exposed the methods Cambridge Analytica used to obtain the Facebook data of 87 million users and use it for targeting Americans with individualized political ads for Donald Trump's 2016 campaign. This time Mark Zuckerberg apologized for "breaching the trust of the users," while adamantly denying it was a data breach.