Abstract: Disclosed is a system that tracks website usage without compromising user privacy. The system aggregates website usage data of multiple users across multiple websites. Website usage data is aggregated in a way that preserves each individual user's privacy. Specifically, information relevant to a particular user may be obtained from the aggregated information without exposing what was actually collected from that user. In some configurations, user-specific website usage data is aggregated using trusted execution environment computing hardware. This ensures that privacy is preserved while user-specific data is transferred to and processed by the system. The trusted execution environment applies differential privacy techniques to ensure that use of the aggregated information does not reveal actual information about a user's website usage history. In this way, privacy is maintained while still enabling many of the scenarios that would otherwise rely on third-party cookies.