Canada's privacy commissioner is probing search giant Google for its inadvertent gathering of data from unsecured Wi-Fi networks while the company was compiling photos for its Street View service.

"We are very concerned about the privacy implications stemming from Google's confirmation that it had been capturing Wi-Fi data in neighbourhoods across Canada and around the world over the past several years," Privacy Commissioner Jennifer Stoddart said in a statement on Tuesday.

"We have a number of questions about how this collection could have happened and about the impact on people’s privacy. We've determined that an investigation is the best way to find the answers."

Google had at first maintained that its Street View cars gathered only public information such as the numeric identifications of Wi-Fi routers, but not the private data — known as "payload" — sent over them while they were driving by homes and businesses. In a blog post on May 14, however, the company admitted that its cars did indeed gather private information, which could include contents of emails.

"It's now clear that we have been mistakenly collecting samples of payload data from open (i.e. non-password-protected) Wi-Fi networks, even though we never used that data in any Google products," the company wrote.

Google said that as soon as it became aware of the problem, it shut down its cars and contacted regulators in various countries to ask how best to dispose of the data it had collected.

Since then, various privacy watchdogs in several countries have announced investigations into the company's actions.

Stoddart's office said it was one of the privacy regulators contacted by Google following the breach. Google has been asked to retain the data it collected in Canada so that it can be studied in an effort to determine what happened, the office said.

A spokesperson for Google Canada said the company is working with the privacy commissioner to answer her questions and concerns.