Google, which is already under fire in Germany, faced a fresh accusation Thursday from government officials of using its camera cars to search for apartment dwellers’ wireless hotspots.

Johannes Caspar, privacy commissioner for the state of Hamburg, said it was illegal to gather the information.

Encrypted WiFi networks or WLANs are often installed in homes to carry phone, radio and data traffic. Although the traffic is usually secure, the signals can leak out through walls onto streets and reveal the name of the WLAN and the MAC or serial number of the device.

Google Germany said it had never been a secret that it was mapping WLANs and denied it was illegal, saying many companies already did this. “It’s not new, and we’re not the only ones doing it,” said spokesman Kay Oberbeck.

A government-funded science agency won a German innovation prize last year for inventing a navigation system that maps all of a city’s WLANs. The Fraunhofer Institute software then uses ordinary phones to guide pedestrians street by street through the city.

Germany’s consumer affairs ministry immediately accused Google of a “dubious” practice, demanding it immediately reveal what data it was collecting on Germans. “They have to lay all the cards on the table,” said a ministerial spokesman.

Caspar, who has the power to impose instant fines but must defend his actions in court, said he was especially concerned that Google collected the SSID or name adopted by each hotspot. Users often name hotspots after themselves, for example “The Schmidt Family.”

Overbeck said Google was not storing information to identify people.

In the past year, both German and Swiss government officials have repeatedly called Google a “data octopus,” objecting to it scanning library books, showing snippets from news websites and taking panorama photos of street frontages all over Europe.