The admission came after the data protection authority in Hamburg, Germany called for an audit of the Wi-Fi data recorded by Google's Street View cars.
Google claims that the data was collected unintentionally because of the accidental inclusion of experimental code in software used by the mobile units to collect Wi-Fi network names and MAC addresses from routers for use by location-based products such as Google Maps for mobile.
According to Alan Eustace, senior vice-president of research and engineering at Google, there was no intention to collect data being sent over the networks.
As soon Google became aware of the problem, the company stripped out the data and began consultations with regulators on how best to dispose of it, he said.
But Germany's data protection authority is not happy with the explanation and has called for a detailed investigation.
A panel of European national data protection chiefs that advises the European Commission is to investigate the matter, according to the New York Times.
The US Federal Trade Commission is also expected investigate whether the data collection breached rules on access to computers and private communications.
In the UK, the Information Commissioner's Office said Google appeared to have breached the Data Protection Act, according to the Financial Times.
But the ICO said it will not be taking any action against Google because it had received assurances from Google that it would delete the data "as soon as reasonably possible".
Observers said the revelations have knocked Google's credibility and the firm's shares were down 0.6% in late New York trading on Monday.