What Facebook knows about you

Thomas Macaulay
Thomas Macaulay

Thomas Macaulay

Tom is a senior online editor across Computerworld UK, Techworld & CIO. He studied English Literature and History at Sussex University before gaining a Masters in Newspaper Journalism from City University. He's particularly interested in the public sector and the ethical implications of emerging technologies.


If the advertisements on your Facebook newsfeed appear remarkably relevant, it's because the social network giant knows better than you might think.

Facebook amassed an estimated $39.9 billion in ad revenue in 2017 by mining its vast troves of data on 2.2 billion users and selling the information to companies that use it to personalise adverts to your individual tastes.

There are also more sinister ways that companies use the data. 

Cambridge Analytica harvested data from an estimated 87 million Facebook users and used the information to send them targeted campaign ads that appealed to their personal prejudices. Critics claim that the strategy helped Donald Trump reach the White House.

Such strategies Wikileaks founder Julian Assange called Facebook "the most appalling spying machine that has ever been invented," in an interview with Russian news site RT.

"Here we have the world's most comprehensive database about people, their relationships, their names, their addresses, their locations and the communications with each other, their relatives, all sitting within the United States, all accessible to US intelligence," claimed Assange.

"Every time you go to a party and take a picture and post that picture to Facebook, you're being a rat," he added at a book launch in 2014.

But even his organisation can't resist joining the mischief. Wikileaks has its own Facebook page with more than 3.5 million followers.

Facebook collects a disturbingly detailed dataset of its users and it hasn't always been transparent about exactly how it's used.

Read next: What Google knows about you – and how to make it forget

Additional reporting by Laurie Clarke