When you install a web browser that claims to block trackers, you might think that would stop websites spying on your browsing activity.

If so, you’d be wrong. As tracking protection becomes a table-stakes feature in more web browsers including Apple’s Safari, Mozilla Firefox, and Microsoft Edge, the targeted ad industry has found a way to circumvent those measures. It’s called “bounce tracking” or “redirect tracking,” and it involves hiding trackers inside the links you click on, making them harder to block without breaking websites.

“Anybody who runs an ad network is almost certainly doing some version of this,” says Peter Snyder, director of privacy at Brave, which has made privacy a central feature of its web browser.

While bounce tracking isn’t the only way websites can evade web browsers’ privacy controls, it’s received less attention than other tactics such as fingerprinting, which involves identifying users via their computers’ unique attributes. Even so, some browser makers say bounce tracking has become a widespread issue, and now they’re finding new ways to fight back.

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