The app then harvested their personal data and that of their friends, their friends friends, friends of friends of friends and so on. Most of the people caught up in the data mining exercise never consented to it or even had any idea it was going on.

Kogan passed the information on to Eunoia Technologies, the company that went on to form Cambridge Analytica. Cambridge Analytica, which was funded by wealthy US Republican donor, Robert Mercer, and headed by Stephen Bannon, has been under scrutiny for at least a year over its use of "hypertargeting" voters as part of Donald Trump's campaign.

Although Facebook was made aware of the breaches in 2015, directing CA to delete the information, it chose not to make the data leak public.

While, at first glance, CA appears to be the bad guy in this story the fact is Facebook facilitated an enormous breach of trust.

None of the estimated 2.2 billion users was ever told the odds were their private information would be handed over to political mercenaries and sold off to the highest bidder. If it was, it was well buried in fine print.

As a $US500 billion plus company, Facebook has more resources to protect its clients than most organisations. Its failure suggests a high degree of naivety on the one hand and potentially indifference on the other.

It has paid dearly with the share price plummeting by more than five per cent in recent days. This has wiped more than $US60 billion off the value of the company.

It also faces the prospect of class actions, breach of privacy investigations - including at least one to be spearheaded by Australian Information Commissioner, Timothy Pilgrim, and the possibility of heavy fines.

Mr Zuckerberg is learning the hard way that when billions of people put their trust in you there will be heavy consequences if you let them down.

He would be keenly aware that just as Facebook wiped the floor with networks such as Sixdegrees and Livejournal back in the day, it is equally vulnerable to a loss of public confidence and support.

While the Cambridge Analytica scandal is not necessarily an existential crisis for Facebook it should serve as a wake up call on the importance of maintaining trust.

Social networks need their members more than their members need social networks. They can't exist without them.