Embarrassed Facebook CEO Mark Zuckerberg apologised this week after 50 million users had their profiles harvested for personal information. He promised tighter controls on data collection, but could this be a game-changer moment for the social media giant

In the shadowy world of online political campaigning uncovered this week, it was hard to know what was real and what was pure make-believe. Could online political consultants dig deep into our souls, using information gathered through social media, and use their knowledge to influence our voting behaviour?

Could they gauge our political mood by our food preferences, or whether we like a particular brand of motorcycle?

Facebook found itself plunged into controversy as news broke that a political consultancy that allegedly used highly dubious methods had harvested up to 50 million Facebook profiles of users.

By gathering information about the users, including their likes, Cambridge Analytica boasted that it could build elaborate psychological profiles that could be used to sway elections.

As a whistleblower employed to work on the project put it, they built models to exploit what they knew about the voters — and targeted their “inner demons”.

By hoovering up as much personal information as possible, they could play on emotions and send voters the right political messages.

The colourful, upper-crust boss of Cambridge Analytica, Alexander Nix, described this approach to campaigning as a “secret sauce”. But revelations on Channel 4 News about the skulduggery allegedly employed by the company — including promising to use “beautiful” Ukrainian women to entrap politicians and a panoply of other dirty tricks — led to Nix’s suspension.

More significantly, it led to concerns about how Facebook handles the personal information it gathers and profits from. It is also likely to prompt questions about whether intrusive “micro-targeting” techniques of campaigning should be allowed in referenda and elections.

For many people, Facebook has become an indispensable (if occasionally annoying) way of keeping in touch with friends and family. But many of these users may not realise that Facebook is perhaps the most effective mass-surveillance tool ever invented, containing infinitely more personal information than the CIA or the KGB could ever dream of.

It is all free for users, but as at least one observer remarked this week, when you get a service free online, you become the product, there to be hawked to advertisers.

Cambridge Analytica claimed to be able to refine personal information gleaned from Facebook. Executives told an undercover reporter, posing as a fixer for a Sri Lankan politician, how they had worked in more than 200 elections across the world, including inn Nigeria, the Czech Republic, India and Argentina.

They said they used data from social media to play on voters’ fears during campaigns and took credit for helping to elect Donald Trump (below).

One of the executives, Mark Turnbull, said: “Our job is to drop the bucket farther down the well than anybody else, to understand those really deep-seated, underlying fears and concerns.”

There is nothing new about targeting specific groups of voters through ads on Facebook or other social media.

In 2012, Barack Obama used micro-targeting to send messages to potential voters by building up an elaborate database of supporters and their Facebook friends.

With the consent of supporters, they targeted social media friends, trying to persuade them to come out to vote.

Although their effectiveness is unknown, both sides in the upcoming abortion referendum campaign in the Republic are paying for promoted posts on Facebook, sometimes targeting specific groups.

Craig Dwyer, a social media manager, said: “Micro-targeting on social media is not a new phenomenon at all, but people have mostly seen it in ads for things like socks and flights. I think we

Piece by piece, Lego brick by Lego brick, the information forms a profile of you