Most Facebook users are unaware the social media giant is tracking their personal traits and interests and listing them for advertisers on its website, according to a new study by the Pew Research Center.
The survey found that nearly three-quarters of respondents were unaware the social media network harvested a list of their interests and traits for the purpose of targeted advertising, according to Tech Crunch.
Facebook users queried by Pew only became aware of this when researchers suggested they view their ad preferences on the social networking site. Of those surveyed, 88% had shared personal material with advertisers. Pew surveyed 963 Facebook users last fall in the U.S. ages 18 and older.
Last month, a separate report showed that Facebook had made user data available to tech companies, including Amazon, Microsoft, and Sony. The company shared email addresses of users’ friends, and also provided Netflix and Spotify access to users’ private messages.
According to Pew’s director of internet and technology research, Lee Rainie, most Americans value privacy but don’t fully understand how that transfers over to their online activity. “The fact that 74% of Facebook users didn’t know that these lists were maintained on them cuts to the heart of that question of where Americans are, or are not, with these systems,” Rainie told the New York Times.
More than half of those surveyed were given a political label by the company. This practice came under fire during the 2016 presidential election when the data-mining firm Cambridge Analytica collected Facebook user data used Facebook data in an effort to influence the election.
Fortune contacted the Pew Research Center and Facebook for comment.