This site, like many others, uses Google Analytics to track user behavior.
Google Analytics is a web analysis service provided by Google. Google collects, organizes, and provides visualizations of anonymized data gathered during a user’s browsing session. Data may include navigation patterns (including links clicked and pages visited), region of origin (based on IP), traffic source (ex. referrals), browser type, and screen size.
Google may use this data to contextualize and personalize the ads of its own advertising network.