A ruling by Germany’s Federal Supreme Court (BGH) has reignited the legal battle over the legitimacy of ad blockers, potentially setting the stage for a precedent that could restrict user control over digital content and privacy tools.
In its decision, the court raised the possibility that ad blockers might unlawfully interfere with copyright-protected elements of websites, including computer program components.
The case centers on a dispute between Axel Springer SE, a major German media publisher, and Eyeo GmbH, the developer behind Adblock Plus. For over a decade, the two sides have been locked in litigation involving both competition and copyright claims. While Eyeo has largely prevailed in earlier decisions, this latest development suggests a significant shift in legal interpretation.
At the heart of the case is whether browser-based ad blockers infringe on publishers’ copyright by altering or suppressing certain elements of web pages. The BGH has taken particular interest in how ad blockers interact with the browser’s Document Object Model (DOM) and CSS Object Model (CSSOM), data structures generated from the HTML and CSS code of websites. These structures are used by the browser to render web pages, and the court noted that ad blockers interfere with them to prevent the display of advertisements.
Axel Springer argued that these dynamic page structures represent protected expressions of computer programs under §69a of the German Copyright Act (UrhG). The company claimed that altering these structures amounts to unauthorized modification and reproduction of a protected program, as described under §69c Nr. 1 and 2 UrhG. The BGH did not confirm the infringement but found that the lower court had insufficiently examined whether elements such as the bytecode executed by the browser engines constitute protected works and whether ad blockers unlawfully alter or reproduce them.
The BGH has now overturned parts of the 2023 decision from the Hamburg Higher Regional Court and returned the case for further fact-finding. Specifically, it instructed the court to determine whether the ad blocker constitutes an “unauthorized modification” or “altered reproduction” of a computer program, and to examine more closely the technical mechanisms involved, particularly how virtual machines in browsers generate object code from bytecode.
This technical emphasis significantly raises the stakes not only for ad blockers but potentially for a broad range of browser extensions. If dynamic rendering processes like DOM and CSSOM manipulations are deemed copyright-protected, then any extension that modifies or filters page content, such as those improving accessibility, blocking trackers, or enhancing security, could be at legal risk.
Axel Springer, the plaintiff, is one of Europe’s largest digital publishing houses, operating major news platforms such as Bild and Welt. The company has long opposed ad blocking, viewing it as a direct threat to its ad-driven revenue model. Eyeo, by contrast, positions Adblock Plus as a privacy and user-control tool, one that empowers individuals to decide what content loads in their browsers.
A public statement authored by Mozilla’s legal director Daniel Nazer warns that the BGH’s stance could lead Germany to become the first democratic country to effectively ban ad blockers, joining China, which has already imposed such restrictions. Mozilla emphasized that such a move would endanger user freedoms, hamper security, and chill innovation in web customization tools.
The next phase of the case will play out in the Hamburg courts, likely over the next one to two years, as judges gather the technical evidence required by the BGH. Until then, the legality of ad blockers in Germany remains uncertain, with the broader implications rippling far beyond a single browser extension.
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