Google says it has scooped up snippets of people's online activities broadcast over unprotected Wi-Fi networks during the past four years.
The admission made Friday is likely to raise more worries about potential privacy breaches as Google gathers volumes of personal information through its search engine and other services.
Google picked up fragments of e-mails and Web addresses while its cars were photographing neighborhoods for the "Street View" feature on its mapping service.
The company says it only recently discovered it has accumulated about 600 gigabytes of data transmitted over public Wi-Fi networks in more than 30 countries. Google says none of the information has appeared in its search engine or other services.