Exposing the Invisible Web: An Analysis of Third-Party HTTP Requests on 1 Million Websites

Timothy Libert


This article provides a quantitative analysis of privacy-compromising mechanisms on 1 million popular websites. Findings indicate that nearly 9 in 10 websites leak user data to parties of which the user is likely unaware; more than 6 in 10 websites spawn third-party cookies; and more than 8 in 10 websites load Javascript code from external parties onto users’ computers. Sites that leak user data contact an average of nine external domains, indicating that users may be tracked by multiple entities in tandem. By tracing the unintended disclosure of personal browsing histories on the Web, it is revealed that a handful of U.S. companies receive the vast bulk of user data. Finally, roughly 1 in 5 websites are potentially vulnerable to known National Security Agency spying techniques at the time of analysis.


behavioral tracking, hidden Web, advertising, Internet policy, Do Not Track

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