BERLIN (Reuters) -Germany's top court ruled on Thursday that law enforcement officials can use secretly installed spy software to monitor phones and computers only in cases that involve serious crimes.

German digital rights group Digitalcourage had complained that a 2017 reform allowing police to monitor encrypted chats or messaging services like WhatsApp in certain circumstance with spy software could also affect people who were not suspects.

The 2017 reform to the criminal procedure code left the areas where surveillance would be used too open, said the court.

According to the court, such surveillance is considered serious interference and thus can only be used for looking into especially heinous crimes.

As a result, police cannot monitor telecommunications when investigating crimes that carry a maximum sentence of three years as they are not serious enough.

Investigators' authority to secretly search suspects' computers and smartphones is partially incompatible with Germany's Basic Law, said the court, but these provisions will remain in effect until new regulations are enacted.