In 2011, the CNIL (Commission nationale de l'informatique et des liberts), fined Google $123,000 over the collection of personal data, including passwords and the content of electronic messages, from home and other WiFi networks by Google's Street View cars as they circulated collecting photos for the company's mapping service.
Google was supposed to have destroyed the information, but said it discovered after a manual Street View disk inventory this month some of the data remained in its possession, ZDNet reported Tuesday.
CNIL said it was reopening its investigation into the company following the discovery of the data.
Google also notified the British data watchdog agency, the Information Commissioner's Office, that it still possessed data relating to British WiFi networks and requested it be allowed to delete the data in question, a request refused by the ICO.
"Like its British counterpart, the CNIL has asked Google to make the data in question available, and to keep it secure for the duration of all necessary investigations," the French authority said in a statement.