Google was under fire after it was revealed the Internet giant's ad-targeting "cookies" bypassed track-blocking software on Apple's web browser for iPhones and computers.
Snippets of code called "cookies" from Google three online ad specialty firms slipped past tracker-blocking safeguards on Apple's Safari browser, Stanford University graduate student Jonathan Mayer said on Friday in a blog post.
"Some privacy researchers and advocates have characterized the interplay between third-party web trackers and browser privacy measures as a 'cat and mouse game' or 'arms race,'" Mayer said.
"This research result regrettably affirms that view as reality for, quite possibly, millions of users."
Safari is the most widely used browser on mobile devices and the default browser on iPhones and Macintosh computers. The Apple browsers are pre-set to block tracking cookies.
Google discontinued use of the offending cookies after Mayer's findings went public, and defended itself against outrage over what it characterized as an unintended side-effect of an effort to safeguard online privacy.
Google last year began using cookies in Safari browsers to let people signed into Google accounts get personalized services, such as being able "+1" ads or other online content as likeable for friends at its online social network.
Specialized cookies were crafted to be set temporarily in Safari browsers to check whether a user was signed into a Google account and had opted for personalized services such as social ads from DoubleClick.
The plan was purportedly to provide users personalization they requested while disclosing no information about them to Google-owned ad specialty firm DoubleClick.
Google reportedly did not realize was the presence of the cookies opened Safari browser doors to a slew of DoubleClick ad tracking cookies, which would otherwise have been rejected.
"The Safari browser contained functionality that then enabled other Google advertising cookies to be set on the browser," the California company said in a released statement.
"We didn't anticipate that this would happen, and we have now started removing these advertising cookies from Safari browsers," it continued.
"It's important to stress that, just as on other browsers, these advertising cookies do not collect personal information."
US legislators and privacy advocates lashed out at Google, accusing the company of trampling on people's privacy and calling for an investigation.
"Google has clearly engaged in 'unfair and deceptive' practices," said Consumer Watchdog privacy project director John Simpson, Consumer Watchdog's Privacy Project director.
"They have been lying about how people can protect their privacy in their instructions about how to opt out of receiving targeted advertising."
Consumer Watchdog fired off a letter to the US Federal Trade Commission calling for an investigtion.
"We are taking immediate steps to address concerns and we are happy to answer any questions regulators and others may have," a Google spokesman told AFP.
Senator John Rockefeller, chairman of the Committee on Science, Commerce, and Transportation, issued a statement vowing to look into how extensively Google and other firms circumvented do-not-track mechanisms in Safari browsers.
"Google knows the rules and simply chose not to follow them in this case," said Association for Competitive Technology president Jonathan Zuck.
"The ongoing irony is that these missteps, intentional or otherwise, invite regulatory action that doesn't hurt Google, but makes it harder for small business competitors to survive."