An additional problem for Google is that it made those unique identifiers accessible to anyone through Google.com - a fact that was discovered by security consultant Ashkan Soltani.
The availability of this data raised a number of concerns with privacy advocates, who maintain that it can be misused to map the movements of individuals.
The data has been recently removed by Google, and the company has refused to comment on the matter, says Cnet.
This is not the first time Google has been accused of harvesting this type of data. The French data protection authority has also investigated in the matter and reached the same conclusion. Google was ordered to pay a fine of 100,000 euros but, obviously undeterred by the obligation to pay such a small amount, continued the practice.
The US Federal Trade Commission also investigated these claims last year, but it all ended with Google's promise that it will stop collecting Wi-Fi data with its Street View cars and no fine for the company.