The rapid growth in the use of social media has had a lot to do with the almost effortless way in which friends and family can keep in touch. A big part of its popularity rests on the fact that it costs nothing to use. But there is no such thing as a free lunch. As has become startlingly clear in recent weeks, the hundreds of millions of social media users, not least of Facebook, the dominant provider, are having data about themselves, often highly personal information, harvested by banks of powerful computers.

Much has been written in recent years about big data and how it can be “mined”. Less attention has been given to the nature of those data. The assumption was that they were perhaps something to do with financial market statistics or corporate performance. The reality, however, is that most of the many petabytes of data (one petabyte is the equivalent of 1.5 million CD-ROM disks) is held on individuals and it is this vast amount of information that has made the social media giants rich.

They earn their living by selling detailed profiles of named individuals to marketing organizations. They monitor what someone looks at with their web browser, not simply on a social media platform. Thus if, for instance, a web page about a new flatscreen TV or automobile has been looked at, an advert for that product will pop up on their social media account. While this may seem harmless enough - indeed it might actually be useful for a user - more alarming personal data are also being harvested. These are being used or arguably abused in elections with data-mining companies making fortunes by providing political parties with intimate profiles of potential supporters or opponents.

In the US, the allegation is that Russian hackers sought to influence the result of the presidential election with fake news and phony social media sites. In the UK it is said that the Brexit vote was influenced by data miners, including the now demonized Cambridge Analytica.

It has long seemed that young people in particular did not care about the amount of personal detail they were sharing in cyberspace on their social media sites. But already their lack of discretion is coming back to haunt them. Nothing ever disappears from cyberspace. Thus potential employers are able to trawl back through years of posts to see what a job applicant has been up to. The US has also announced that it will be checking social media when it comes to processing visa applications. Such checks are essentially benign but for governments and organizations that have less honorable requirements, the huge quantities of data already out there will prove a rich resource.

On Tuesday, Mark Zuckerberg gave evidence to Congress. Media hype predicted the legislators would roast the Facebook boss for the platform’s failure to protect the details of 87 million users. In the event, Zuckerberg was lightly grilled and nobody questioned Facebook’s core business model that is precisely the sale of those details to third parties.

Maybe Congressmen were thinking that Facebook is an outstanding American success story that gives Washington indirect leverage of a global scale. To perpetuate the scandal of the allegedly abused data would actually be to condemn the very way in which Facebook makes its money.