The trouble was that the software used for that part of the task had been created for a different purpose, and it logged the payload of the Wi-Fi packets (ie, the actual data being transmitted) as well as the information about the access point. If an access point wasn't set to use encryption and personal or sensitive data happened to be flowing as a Street View car drove by, that data would have been recorded.
According to reports, the data captured included emails, usernames and passwords.
This, understandably, caused a fuss when Google revealed what had happened. The company worked with local privacy regulators such as Australia's Privacy Commissioner to ensure that the data was deleted in an acceptable manner.
Ironically, Google handed over to regulators in Germany, France and Spain the the data it had mistakenly collected. In March, Google was fined â‚¬100,000 by CNIL, the French authority for the protection of privacy and personal data, for failing to respond to its requests in a timely manner.
Other countries were more sensible - please read on.