Over the weekend, you might have noticed a sharp increase in the number of people complaining about how we just can’t trust Facebook. And if you didn’t, you probably should have been paying more attention, because there’s been a pretty big development on that front.

You know that one friend who’s always warning you that Facebook is harvesting all your data to subtly manipulate your thoughts? As it turns out, they were kind of right. The Guardian and other outlets reported on the weekend that a company called Cambridge Analytica has been using Facebook data to form complex psychological profiles of voters in both the UK and the US, and then target them with with political ads designed to subtly manipulate them into voting a certain way.

Cambridge Analytica was most famously used by Donald Trump in his successful campaign for President back in 2016.

The controversial program affected around 50 million people, and most of them never knew their data had been taken. If you’re a Facebook user, you could be one fo the millions caught up in the whole thing. Here’s what’s going on:

Using Personality Quizzes To Get Access To Facebook Data

In 2014, a guy called Dr. Aleksandr Kogan made a personality test app called thisisyourdigitallife, which was downloaded by around 270,000 people. By downloading that app, those people gave Kogan permission to access data they shared on Facebook — things like what city they lived in and pages they liked and shared — though they were under the impression it was for academic use only.

If that scares you, this is a great reminder to actually read terms and conditions, and those permission request screens that pop up when you install games and apps on Facebook. You may just discover that some of the apps you’ve been using are also using your data for more than just a fun quiz.

Kogan’s app went a step further though, by mining the data of people who weren’t actually using it. People who agreed to use the app were unwittingly giving it access to the profiles of their Facebook friends too, meaning millions of people’s Facebook data was harvested without them knowing, let alone consenting.

All in all, Kogan ended up with the data of around 50 million people. And rather than just keep it for his own personal research, he sold it to a group called Cambridge Analytica.

Who Are Cambridge Analytica, And What Did They Do With The Data?

Cambridge Analytica are a data analysis firm for hire. Basically, they specialise in using what they’ve learned from big sets of data to manipulate people’s behaviour, and they do this for whoever pays them.

As Christopher Wylie, the former Cambridge Analytica employee who blew the whistle on all this, told The Guardian: “It is a full service propaganda machine. If you can control all of the streams of information around your opponent, you can influence how they perceive that battle space, and you can then influence how they’re going to behave and react.”

That includes influencing how people vote in elections. Cambridge Analytica worked with both Trump’s election team and the Brexit campaign, and used the psychological profiles they were able to build based on people’s Facebook likes to serve them extremely targeted content designed to sway their views.

Basically, millions of people may have unknowingly been part of a massive experiment designed to subtly manipulate them into voting a certain way. Cambridge Analytica almost got away with it, too. When questioned repeatedly about it previously, they denied even having access to Facebook data. We only know about this because Wylie broke a non-disclosure agreement to blow the whistle on it, and a reporter called Carole Cadwalladr endured months legal threats and abuse while trying to cover the story.

What Was Facebook’s Role In This?

Facebook denies that any of this constitutes a data breach. They maintain that Kogan’s app gathered information “in a legitimate way”, and that their rules were only breached when he passed that data on to third parties like Cambridge Analytica.

People aren’t particularly happy with this response though, because they feel Facebook could have done much, much more. It took almost two years for them to start cracking down on the different groups the data was passed on to, and according to documents provided by Wylie, they pretty much just asked those groups to check a box saying they’d deleted it, without checking that it actually was deleted.

More pressingly, though, Facebook didn’t tell the users whose data had been used that their information had been harvested. This potentially breaks laws in the UK and the US, and is being investigated at the moment.

MySpace: We’re a social network.

Facebook: We can do that too!

SnapChat: We let you send disappearing messages.

Facebook: Great idea!

Venmo: We let you send mon—

Facebook: Us too!

Governments: We’d love to meddle in elections.

Facebook: DO IT WITH FACEBOOK!

— jordan (@JordanUhl) March 18, 2018

There’s much more to this story, which you can read about at length here, but that’s the gist of it: a company was able to use huge quantities of Facebook data to manipulate people’s voting preferences without their permission, and people are, quite rightly, real mad about it.