Google claims that it has never analyzed or reviewed in detail the content of the data collected since 2007, according to US reports.

When the collection of WiFi data was exposed by an audit ordered by German privacy authorities, Google said the data had been collected unintentionally by experimental code included "by mistake" in software used by Google's Street View cars.

"Maintaining people's trust is crucial to everything we do, and by mistakenly using code that collected payload data, we fell short," Google's director of public policy, Pablo Chavez, said in a letter to Congress.

"We are determined to learn all the lessons we can from our mistake," he said.

But, Joe Barton, Republican representative from Texas, has called for a congressional hearing on the matter.

"Google now confesses it has been collecting people's information for years, yet claims they still do not know exactly what they collected and who was vulnerable. This is deeply troubling for a company that bases its business model on gathering consumer data," Barton said in a statement.

"As we are contemplating privacy legislation in the committee, I think this matter warrants a hearing, at minimum," Barton continued.

Privacy International is planning to file a criminal complaint with the UK police after Google published an audit by third-party computer forensics experts.

Privacy International said the report indicates that the interception was deliberate and contravenes UK wiretapping laws.

Police investigations are already underway in Australia and a similar investigation is under consideration in Germany, where an audit by privacy authorities forced Google to admit its Street View cars were collecting Wi-Fi data as well as images.

This article was first published by Computer Weekly