What Is Cross-Site Tracking?

Analysis of cross-site tracking mechanisms confirms that third-party entities—including advertisers and analytics platforms—utilize technologies such as cookies, tracking pixels, and browser fingerprinting to monitor users across multiple unrelated websites. Empirical evidence demonstrates that:

• Cookies are the most prevalent tool, with third-party cookies embedded in over 80% of popular websites, facilitating the sharing of behavioral data with external domains.
• Tracking pixels (1x1 invisible images) and browser fingerprinting further extend tracking capabilities by uniquely identifying users without reliance on cookies.
• A notable finding reports that nearly 75% of tracking activities begin prior to users providing any form of consent, often before users interact with cookie banners.

Key results highlight privacy concerns—users are subject to the creation of detailed behavioral profiles for targeted advertising, frequently without their knowledge or explicit approval. Interviews and user studies consistently demonstrate low awareness of the scale and methods of cross-site tracking (Utz et al., 2019).

Regulatory responses include the General Data Protection Regulation (GDPR), which mandates consent for data collection and has led to observable shifts in tracking practices. However, analyses reveal that even post-GDPR, third-party tracking remains prevalent due to technical workarounds and non-compliance (Matte et al., 2020).

Summary of findings:

• Cross-site tracking is primarily driven by advertisers’ need for targeted marketing.
• Technical tools (cookies, pixels, fingerprinting) enable persistent monitoring.
• The vast majority of tracking commences before user consent mechanisms are presented.
• Regulatory measures have not fully eliminated stealth tracking practices.
• Ongoing research calls for stronger enforcement and new technical safeguards.