Privacy concerns have swamped Facebook since it acknowledged last month that information about millions of users wrongly ended up in the hands of political consultancy Cambridge Analytica.
The firm that has counted US President Donald Trump’s 2016 electoral campaign among its clients.
Zuckerberg said on Wednesday under questioning by US representative Ben Lujá* that, for security reasons, Facebook also collects “data of people who have not signed up for Facebook posts.”
Legislators and privacy advocates immediately protested the practice, with many saying that Facebook needed to develop a way for non-users to find out what the company knows about them.
“We’ve got to fix that,” representative Lujá* , a Democrat, told Zuckerberg, calling for such disclosure, a move that would have unclear effects on the company’s ability to target ads. Zuckerberg did not respond. On Friday Facebook said it had no plans to build such a tool.
Critics said that Zuckerberg has not said enough about the extent and use of the data.
“It’s not clear what Facebook is doing with that information,” said Chris Calabrese, vice president for policy at the Center for Democracy & Technology, a Washington advocacy group.
Facebook gets some data on non-users from people on its network, such as when a user uploads e-mail addresses of friends. Other information comes from “cookies,” small files stored via a browser and used by Facebook and others to track people on the internet, sometimes to target them with ads.
“This kind of data collection is fundamental to how the internet works,” Facebook said.
Asked if people could opt out, Facebook added: “There are basic things you can do to limit the use of this information for advertising, like using browser or device settings to delete cookies. This would apply to other services beyond Facebook because, as mentioned, it is standard to how the internet works.”
Facebook often installs cookies on non-users’ browsers if they visit sites with Facebook “like” and “share” buttons, whether or not a person pushes a button.
Facebook said it uses browsing data to create analytics reports, including about traffic to a site.
The company said it does not use the data to target ads, except those inviting people to join Facebook.
Advocates and lawmakers say they are singling out Facebook because of its size, rivalled outside China only by Alphabet’s Google, and because they allege Zuckerberg was not forthcoming about the extent and reasons for the tracking.