Germany's High Court has banned police from installing spyware on computers of suspected criminals without their knowledge.
The decision, announced Monday, is a blow to the plans of the German Interior Minister Wolfgang Schäuble to give the Federal Criminal Police Office (BKA) greater power to monitor terrorists and other criminals online, and peek inside their computers.
Two other federal judges had differed over whether police should be able to hack into the computers of suspected criminals and install spyware. In February, one judge approved police hacking. But another barred the practice in November, resulting in an appeal by federal prosecutors.
The High Court in Karlsruhe argued that searching computers is similar to searching homes, a practice in Germany that requires police to follow certain procedures, such as obtaining a search warrant and informing suspected offenders of a search.
The judges also argued that hacking computers by the police is not permitted under Germany's strict phone-tapping laws and that legislation would be needed to enable covert surveillance.
Last year, Schäuble persuaded the German parliament to approve €132 million (£87m) for his Programme for Strengthening Domestic Security.
As part of the programme, the BKA would have been allowed to penetrate and monitor PCs of suspected offenders in Germany via the internet.
It also calls for greater use of video cameras in public places, biometric systems and other new security technologies, as well as the establishment of an "Internet Monitoring and Analysis Office."