Google scooped up sensitive data such as passwords when putting together its Street View service, suggests an early look at the information.
The examination was carried out by French data protection agency CNIL as it decides whether to prosecute the search firm for gathering the data.
The data was gathered as Google logged wi-fi hotspots to help it develop location-based services.
Previously, Google said there was "no harm, no foul" in collecting the data.
CNIL, like many other data protection agencies worldwide, asked Google to hand over copies of the data it gathered to find out if privacy laws had been breached.
CNIL chairman Alex Turk said Google handed the data to the agency on 4 June following an official request and it was now in the process of combing through the reams of information.
Talking to reporters as CNIL unveiled its annual report, Mr Turk said the early look showed the presence of "data that are normally covered by... banking and medical privacy rules".
Tech news site IDG reported that CNIL had spotted passwords for e-mail services and chunks of text from messages in its first glance at the data.
Mr Turk said he hoped to be able to decide by September if Google had a case to answer for breaching privacy. CNIL has the power to hand down a warning, levy a fine or pass the case to a prosecutor to see if a criminal charge is warranted.
Google said it was working with the French authorities and many others and would delete the information it had gathered if asked.
"We have reached out to the data protection authorities in the relevant countries, and are working with them to answer any questions they have," a Google spokesperson said.
"Our ultimate objective is to delete the data consistent with our legal obligations and in consultation with the appropriate authorities," added the spokesperson.
The row has blown up following Google's admission that its Street View cars "accidentally" grabbed data from unsecured wi-fi networks as the vehicles were snapping stills of street scenes in 30 nations. Google has now stopped gathering information about wi-fi networks.
The revelation has led to investigations in Germany, Spain, Italy, Australia, New Zealand and Canada. Several US states are considering filing civil suits for damages over the collection of the data. US digital rights groups have called for an official "probe" into the issue.
Google has defended its collection of the data saying it was done "accidentally". Google boss Eric Schmidt said there was "no harm, no foul" in collecting the snippets of information.
"Who was harmed? Name the person," Mr Schmidt said at during an interview at the company's annual Zeitgeist conference held in Watford in mid-May.
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