Google has admitted it has discovered more Wi-Fi data collected by its Street View cars that it has failed to delete in an embarrassing incident for the firm.
Google has been caught in a huge privacy storm ever since the Wi-Fi sniffing incidents came to light, in numerous countries including the UK.
This has led to police investigations and action by the Information Commissioner's Office (ICO) against the firm, although no fines or legal action has ever been taken.
Google had previously claimed to have deleted all the data it had gathered in the UK, but in a letter on Friday to the ICO, its global privacy counsel Peter Fleischer admitted yet more information had been found.
"Google has recently confirmed that it still has in its possession a small portion of payload data collected by our Street View vehicles in the UK. Google apologises for this error," he said.
Fleischer explained that the data had only now been uncovered due to a scan of the disks that had been used to house the information the car had collected.
"In recent months, Google has been reviewing its handling of Street View disks and undertaking a comprehensive manual review of our Street View disk inventory. That review involves the physical inspection and re-scanning of thousands of disks," he said.
"In conducting that review, we have determined that we continue to have payload data from the UK and other countries. We are in the process of notifying the relevant authorities in those countries."
Fleischer also asked the ICO what it wanted the firm to do with the data, before it took steps to delete it.
The ICO said it was "cause for concern" that the data had not been deleted, despite having been collected prior to 2010.
It said Google had breached its undertaking with the ICO by failing to delete the data, opening itself up for a £500,000 fine.
"Google must supply the data to the ICO immediately, so that we can subject it to forensic analysis before deciding on the necessary course of action," an ICO spokesperson added.
"We are also in touch with other data protection authorities in the EU and elsewhere through the Article 29 Working Party and the GPEN network to coordinate the response to this development."
Privacy advocates and MPs have been highly critical of the ICO's handling of the Street View investigation, with the latest revelations likely adding to their outrage.
Dan Worth is the news editor for V3 having first joined the site as a reporter in November 2009. He specialises in a raft of areas including fixed and mobile telecoms, data protection, social media and government IT. Before joining V3 Dan covered communications technology, data handling and resilience in the emergency services sector on the BAPCO Journal.