Germany’s highest court on Thursday ruled that law enforcement cannot use spyware to monitor personal devices in cases that carry less than a three year maximum sentence.

The court was responding to a lawsuit brought by the German digital freedoms organization Digitalcourage. 

The plaintiffs argued that a 2017 rules change enabling law enforcement to use spyware to eavesdrop on encrypted chats and messaging platforms could unfairly expose communications belonging to people who are not criminal suspects.

The 2017 change to the German criminal procedure code was not precise enough about when spyware can be used, the court ruled, saying that snooping software is only appropriate in investigations of serious cases.

Such surveillance causes a “very severe interference” with fundamental rights, the court said in a press release.  

Law enforcement use of spyware “enables the interception and analysis of all raw data exchanged and thus has an exceptional reach, particularly given the realities of modern information technology and its significance for communication relations,” the press release said.