The German Chaos Computer Club has uncovered two recent instances of police using "trojan" spying programs on the computers of suspects they later arrested.
The programs allowed remote users to take over webcams, eavesdrop on internet phone calls and take screenshots of the user's activity every 30 seconds.
Some of those activities, if they took place, would have breached the law in Germany, which only allow authorities to tap computers for phone calls.
Hans-Peter Friedrich, the German interior minister, said the government would re-examine the software it was using but that internet telephone monitoring would continue.
Nick Spicer reports from Berlin.
Source: Al Jazeera