Privacy activist on a mission to find out what Facebook knows about him

How your data makes Facebook billions
How your data makes Facebook billions

Do you have a right to know who's watching you on the internet, and how? That's the question a privacy activist is posing with a campaign to get Facebook to tell him everything it knows about him.

Paul-Oliver Dehaye will appear before a British parliamentary committee on Tuesday to talk about his effort, including the latest part of it, a bid to get Facebook to provide him with a list of sites where the company tracks his activity online. Cambridge Analytica whistleblower Christopher Wylie will also appear.

Dehaye asked Facebook in December 2016 for information advertisers gathered about him through a tool called the Facebook pixel.

The pixel is a piece of Facebook code that can be embedded on a third party website. "In short, advertisers use Facebook technologies, such as the Facebook pixel, to help them show adverts to people who have visited their website or used their mobile app," Facebook said in an email to Dehaye.

For instance, a soap brand could target Facebook advertising at people who had visited their website while logged into Facebook.

Related: I downloaded 14 years of my Facebook data and here's what happened

Dehaye wants a list of all the websites that gathered information about him in this way.

"I am worried, for instance, of a candidate having lots of different websites that they track people on to figure out what they care about -- that candidate could then present themselves as a one-issue candidate to all those people," he told CNN Monday.

Facebook told Dehaye that it was "not technically feasible" for them to provide the information he had requested.

Facebook, whose European headquarters is based in Ireland, is subject to Irish and European data protection law. The company cited an exemption in the law that allows it to reject a request like Dehaye's if it "would involve disproportionate effort."

This is not the first request of this nature Dehaye has made of Facebook. In 2016, he wrote to Facebook asking the company to provide a list of all of the organizations that had uploaded information about him to Facebook's Custom Audience tool.

The tool allows advertisers to upload a database of names, phone numbers, and email addresses. Facebook matches the data to personal profiles on its network and lets organizations target those profiles with advertising.

Political campaigns, for instance, can upload a list of email addresses they gather through their websites or at rallies, and can then serve those people with ads on Facebook.

Dehaye can access a list of the organizations that uploaded information about him going back eight weeks, but he says that's not enough.

"There is no reason for it, I want to go back to the US election, I want to go back to Brexit, all those circumstances that there is doubts on how information was used and weaponized," he said.

The Irish Data Protection Commissioner says it is reviewing Dehaye's complaint.

"We receive regular questions from Mr Dehaye about our service and we always do our best to assist him. We also fully comply with our legal obligations to provide him with access to his data," a Facebook spokesperson told CNN.

Dehaye is the founder of personal data management startup PersonalData.IO. He has also provided assistance to a New York professor who is suing Cambridge Analytica for the information it knows about him.

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