The study analyzed survey data from 1,000 participants, two-thirds of whom reported using at least one ad blocker or other program that can prevent websites and third-party companies from tracking their online activities.

“The motivation for people to adopt ad blockers is largely to improve the user experience, as opposed to tackling issues of privacy,” said lead author Arunesh Mathur, a graduate student in the Department of Computer Science. “Most people are adopting ad blockers to speed up their website loading and declutter webpages.” Interestingly, survey respondents cited the same reasons for adopting content blockers, which block both advertisements and tracking.

The survey also showed that users of ad and tracker blockers generally did not have more knowledge about online tracking than people who did not use blockers. Less than half of all respondents were aware of visible outcomes of online tracking, such as targeted ads and website customization. Less than 20 percent were able to recognize invisible outcomes of online tracking such as varying prices or the collection of personally identifiable information, although blocker users were somewhat more likely to understand these outcomes than non-users.

A majority of respondents were uncomfortable with the collection of their online data. However, the researchers wrote, “These participants often expressed apathy, saying that data collection was hard to stop, and that if companies really wanted their data, they could acquire it in different ways.”

The survey included a feature that measured whether participants’ web browsers were blocking third-party trackers or third-party cookies – small pieces of data stored on a user’s computer that help to customize websites. The results showed that only about one-fifth of ad blocker users were also blocking third-party trackers, while the majority of those using content or tracker blockers were indeed blocking trackers. Users can configure ad blockers to disable trackers not associated with ads, but these settings are not enabled by default.

“Because this ecosystem is so convoluted and the manner in which you’re tracked differs a lot not just based on your activities but on where you enter your data, it’s really hard for people to understand what’s going on,” said Mathur. “One of the suggestions we make is that, rather than having users take this action, browsers should do more to protect users from online tracking. They should actively block trackers and not even let it be something that users have to do.” Web browser providers including Mozilla and Apple are taking significant steps in this direction, he added.

Mathur’s coauthors from Princeton’s Department of Computer Science included Associate Professor Arvind Narayanan and Research Scholar Marshini Chetty. Jessica Vitak of the University of Maryland was also a coauthor. The researchers will present their work on August 13 at the Advanced Computing Systems Association’s (USENIX) Symposium on Usable Privacy and Security.