Cross-Site Tracking.

The practice of linking a user's activity across multiple unrelated websites to build a long-lived behavioural profile. It belongs to the Privacy & Data Protection category of cybersecurity.

The practice of linking a user's activity across multiple unrelated websites to build a long-lived behavioural profile.

Cross-site tracking occurs when the same identifier — a third-party cookie, fingerprint, login, or device graph — is read on many sites so that browsing, purchases, and interests can be combined into a single profile. The technique powers behavioural advertising, retargeting, and analytics, but it also enables surveillance and re-identification of supposedly anonymous data. Modern browsers fight cross-site tracking through Intelligent Tracking Prevention (Safari), Enhanced Tracking Protection (Firefox), Storage Partitioning, third-party cookie blocking, and proposals like Privacy Sandbox. Other defences include anti-tracking extensions, separate browser profiles or containers per task, and privacy laws such as GDPR and CCPA that demand consent or opt-out.

Defences for Cross-Site Tracking typically combine technical controls and operational practices, as detailed in the full definition above.

Common alternative names include: Cross-site tracking, Third-party tracking, Behavioural tracking.