The companies used special computer code that tricks Apple's Safari Web-browsing software into letting them monitor many users. Safari, the most widely used browser on mobile devices, is designed to block such tracking by default. Google disabled its code after being contacted by The Wall Street Journal.
The Google code was spotted by Stanford researcher Jonathan Mayer and independently confirmed by a technical adviser to the Journal, Ashkan Soltani, who found that ads on 22 of the top 100 websites installed the Google tracking code on a test computer, and ads on 23 sites installed it on an iPhone browser.
Apple disables third party cookies in MobileSafari by default, a move that breaks with common practice. Google says it did not install the cookies to collect personal information but rather to provide services to its users.
"The Journal mischaracterizes what happened and why. We used known Safari functionality to provide features that signed-in Google users had enabled. It's important to stress that these advertising cookies do not collect personal information."
When Apple was contacted by the journal they said, "We are working to put a stop" to the circumvention of Safari privacy settings.