Google has been fined by German authorities over claims it illegally collected personal data during its Street View project.
The Hamburg data protection office fined the company 145,000 euros (£124,000) for privacy offences, including the collection of emails, passwords and photos.
Google’s specially-equipped cars picked up the data from unsecured wireless networks as they took photos of Hamburg’s streets.
“Among the information gathered in the drive-bys were significant amounts of personal data of varying quality,” said the data protection office.
“For example emails, passwords, photos and chat protocols were collected.
“In my opinion this case constitutes one of the biggest known data protection violations in history,” said the office’s chief, Johannes Caspar.
Google co-operated with the investigation and was also ordered to immediately delete all the private information.
The company said the collection of the data was a “mistake” and a “significant lapse of Google’s internal control mechanisms”.
It said the data was never looked at and that it had already deleted it all.
Google was fined $7m (£4.6m) in March this year for a similar incident of ‘wi-fi snooping’ while working on Street View in the US.
In that case, Google blamed the intrusion on a rogue engineer who it said had rigged a software programme without its permission.
The technology giant is also facing further scrutiny over its privacy policies elsewhere in the EU.
Six European countries are taking legal action to try to force the tech giant to overhaul its privacy practices.
The claim Google’s current policy does not allow users to work out which information is kept, how it is combined by Google services or how long the company retains it.
Google insists its policy complies with European laws.