Trackers are unique codes or values found within web pages and often are used to track user interaction. These codes can be used to correlate a disparate group of websites to a central entity. PassiveTotal's tracker dataset includes IDs from providers like Google, Yandex, Mixpanel, New Relic, Clicky and is continuing to grow on a regular basis.
A quick overview can be found on our RiskIQ youtube.
A detailed use case for this data set can be found on our RiskIQ blog.