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10 November 2011, 16:26

AVM cannot prohibit modification of GPL router firmware

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AVM logo The Regional Court of Berlin has ruled that AVM must tolerate other companies offering software that can modify the GPL-licensed Linux-based firmware of their Fritzbox routers. The decision in the case brought by AVM against Cybits AG rejects AVM's claim that Cybits'German language link Surf-Sitter software, which modified the firmware of their routers, violated copyright and trademark law even when the software in question is licensed under the GPL.

Cybits logo Cybits AG's Surf-Sitter software is parental control software which allows a parent to set times when surfing is allowed or when a web filter is enabled. The software is also available for installation on routers like the Fritzbox; when installing, the application connects to the router and downloads, modifies and reloads the router's firmware onto the device. AVM said that this was a violation of its copyright and in January last year, it obtained a preliminary injunction which prohibited Cybits AG from distributing that software or any other which edited the router firmware or used other parts of that firmware unchanged. At the same time, it filed a case against Cybits.

Harald Welte, Linux developer and founder of, became interested in the case as both AVM and Cybits use iptables/netfilter for which Welte holds intellectual property rights. He joined the case as a third party intervener on behalf of Cybits. Welte considered AVM's actions a GPL violation because they were attempting to stop a third party distributing a modified version of the software. The General Public Licence from the Free Software Foundation specifically allows modifications of GPL-licensed software and allows it to be distributed in modified form. In the hearing, the court focused the dispute on the question of whether a router is more likely to be regarded as a closed system of hardware and software, similar to a phone with a SIM lock with which a manufacturer could prevent modification, or as a computer on which the owner could install additional software.

In its decision, the court rejected the claim by AVM to ban the sale of Cybits software. Both Cybits and other third parties are allowed to make changes to the Fritzbox firmware. Cybits is also not prohibited from selling software which helps the user make those modifications. However, the court did rule in AVM's favour to enjoin Cybit from distributing software which made the router display incorrect or faulty status information. AVM claimed that the use of Cybits software made it appear to the user as if the router had malfunctioned.

Welte said he was extremely pleased with the court's decision saying "Enabling and encouraging everyone to innovate based on existing software and products is a key aspect of the Free Software movement". AVM is encouraged by the ruling as it confirms that the Surf-Sitter for Fritzbox should not be distributed in its current form. According to the judgement, Cybits must prevent its software from interfering with the Fritzbox in sucha way that erroneous displays about the connection and child protection settings appear in the user interface. AVM noted that, as expected, the judgement made no change with respect to the GPL, and says it will "continue its work in the open-source area unabated".

The written verdict is still pending. The decision is not final and the parties can appeal against the decision.


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