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In a landmark decision on March 7, 2024, the European Court of Justice (ECJ) issued a pivotal ruling in case C-604/22, directly impacting the online advertising sector’s approach to data privacy. This ruling not only clarifies the definition of personal data but also expands the understanding of what it means to be a data controller within the framework of RealTime Bidding (RTB) systems used widely across the industry.


Understanding the Background and the TCF


Real-Time Bidding is a digital advertising method where companies bid in real time to place personalised ads based on user profiles. These profiles are crafted using a range of personal data elements such as location, age, search history, and recent purchases. The process hinges on obtaining user consent, aligning with the stringent requirements of the General Data Protection Regulation (GDPR).

IAB Europe, representing Belgian advertising interests, devised the Transparency and Consent Framework (TCF) to ensure GDPR compliance in RTB systems. Central to this framework is the Transparency and Consent String (TC String), an encrypted set of user preferences shared across the ad bidding network. A pivotal aspect here is the linking of the TC String to a user’s IP address via cookies, a process that has raised significant data privacy concerns.


The Belgian Data Protection Authority’s Stance

In 2022, the Belgian Data Protection Authority flagged IAB’s TCF as non-compliant with GDPR, citing the unlawful processing of personal data. The case escalated to the ECJ, posing critical questions: Is the TC String personal data? And, should IAB Europe be considered a data controller?


The ECJ’s Ruling: Clarifying Personal Data and Controllership

The ECJ ruled that the TC String does indeed constitute personal data. Although it does not allow direct identification of a person, it contains sufficient details, such as preferences, that could identify a user when combined with other data like an IP address.

Further, the Court addressed whether IAB Europe functions as a data controller. It concluded that by providing a framework dictating how personal data should be handled, IAB Europe acts as a joint controller. This is because it influences how its members process data and has established rules and penalties for non-compliance, effectively shaping the data processing landscape within its member organisations.


Implications for the Online Advertising Industry

This decision underlines a broader role for organisations like IAB Europe in ensuring GDPR compliance, potentially increasing their liability. Online advertisers using TCF must now clearly indicate in consent banners that the TC String is personal data and that they, alongside the website providers, are joint controllers.

The ruling also limits the extent of liability for further data processing, stating that being a joint controller for initial data processing does not automatically extend to subsequent processing activities by other entities.



The ECJ’s ruling in C-604/22 serves as a crucial reminder of the evolving landscape of data privacy laws and their interpretation. It stresses the need for transparency and stricter compliance with GDPR, ensuring that personal data protection remains at the forefront of the digital advertising industry’s agenda. For industry players, this is a call to align their practices with these clarified legal standards, fostering a more secure and privacy-conscious advertising environment.