The change means not only does Facebook collect data on how you use its site — what pages you visit, how long you read a post, which links you click — but now it also collects data on other websites and apps.
Facebook says the changes will help them better target ads to its users.
"When we ask people about our ads, one of the top things they tell us is that they want to see ads that are more relevant to their interests," the company said in a statement in June.
But these changes have sparked the ire of the EU's privacy watchdog, which argues users should have the choice whether to opt in.
Facebook will track user data on other sites through tools it offers to the owners of third-party websites.
Users do have the option of opting out of the new policy once they are enrolled, either on their iOS or Android device, or through the Digital Advertising Alliance of Canada. Once you opt out, it applies to Facebook products across platforms, including phone, tablet and desktop.
But opting out only goes so far, privacy advocates warn. Andrew Hilts, a researcher at Citizen Lab Internet research group at the Munk School of Global Affairs, said Facebook's opt-out policy affects which ads you see, not what information the company tracks.
"There's a big difference between not using data for personalized ads and not collecting that data in the first place," he said.