An engineer working on an experimental WiFi project wrote a piece of code that sampled all categories of publicly broadcast WiFi data. A year later, the Google mobile team started a project to collect basic WiFi network data like SSID information and MAC addresses using Googles Street View cars. Google says it has been mistakenly collecting samples of payload data from open (i.e. non-password-protected) WiFi networks, even though we never used that data in any Google products. We are profoundly sorry for this error and are determined to learn all the lessons we can from our mistake.”]
Source: https://googleblog.blogspot.com/2010/05/wifi-data-collection-update.html