“It regards suspicions over the interception of data,” prosecution spokesperson Wilhelm Möllers told news agency DDP, adding that investigators are trying to determine whether initial concerns that the company violated paragraph 202b of the criminal code are “resilient.”

The law forbids the unauthorised collection of private data through technical means.

“It remains totally open as to whether or not we will engage in deeper investigation,” he said.

Google had previously said that it was only collecting WiFi network names and addresses with its Street View cars, which cruise cities around the world taking photographs for the Google Maps service. But on Friday Google senior vice president for engineering and research Alan Eustace said in a blog post that the company had “mistakenly” collected a small amount of data fragments from open networks.

The mistake came to light following an audit from the Data Protection Authority in Hamburg, he said, adding it had been caused by a coding error.

Following criticism from data protection advocates, the company grounded its Street View cars and said it planned to delete the information, but has not signalled it is willing to let authorities look at exactly what was collected.

Operations for the Street View navigation program – which gives users photographic view of roads – has already come under heavy criticism in Germany, where privacy laws are fiercely defended.

When news of the WiFi cock-up was revealed, the country’s Consumer Protection Minister Ilse Aigner accused Google of criminal behaviour and called for a transparent investigation.

The California-based company has used Street View cars in more than 30 nations.