Britain's privacy watchdog is to look again at what personal information internet giant Google gathered from private wi-fi networks.
The Information Commissioner's Office had investigated a sample earlier this year after it was revealed that Google had collected personal data during its Street View project.
At the time, it said no "significant" personal details were collected.
But Google has since admitted that e-mails and passwords were copied.
On its official Google blog, senior vice president Alan Eustace wrote that the company was "mortified" to discover, after the initial investigation in May, that personal information had been collected.
Privacy watchdogs in numerous countries, including France, Germany and Canada, had also investigated the information.
"It's clear from those [external] inspections that while most of the data is fragmentary, in some instances entire e-mails and URLs were captured, as well as passwords," Mr Eustace wrote.
"We want to delete this data as soon as possible and I would like to apologise again for the fact that we collected it in the first place.
"We are mortified by what happened, but confident that... changes to our processes and structure will significantly improve our internal privacy and security practices for the benefit of all our users."
A spokesman for the Information Commissioner's Office said it had kept an eye on international investigations since its own one concluded in July.
That investigation said that the information "did not include meaningful personal details that could be linked to an identifiable person".
However, Google's admission of more detailed data has prompted further action by the ICO.
"We will be making enquires to see whether this information relates to the data inadvertently captured in the UK, before deciding on the necessary course of action, including a consideration of the need to use our enforcement powers," a spokesman said.
Google's director of privacy Alma Whitten said the company would work with the ICO to answer its "further questions and concerns".
She added that the data "has never been used in any Google product and was never intended to be used by Google in any way".
Information about the gathering of personal data came to light following a request by data protection authorities in Hamburg, Germany, for more information about the operation of Google's Street View technology which adds images of locations to maps.
This revealed that Google had "accidentally" grabbed data from unsecured hotspots for years as its Street View cars captured images of street scenes. In total it is thought to have grabbed about 600 gigabytes of data.
It led to many data protection authorities pressing Google for access to the mass of data it grabbed to see whether laws on the protecting of personal information had been broken.
Google said it had since "strengthened" its internal privacy and security practices.
Alex Deane, director of privacy campaign group Big Brother Watch, said Google should launch an immediate investigation into how the breach happened.
"As if building up a database of photographs of millions of people's private homes wasn't enough, the news that Google has also harvested e-mail addresses and passwords is nothing short of outrageous," said Mr Deane.