Google will soon know far more about who you are and what you do on the Web.
The Web giant announced Tuesday that it plans to follow the activities of users across nearly all of its ubiquitous sites, including YouTube, Gmail and its leading search engine.
Google has been collecting some of this information. But for the first time, it is combining data across its websites to stitch together a fuller portrait of users.
Consumers won't be able to opt out of the changes, which take effect March 1. And experts say the policy shift will invite greater scrutiny from federal regulators of the company's privacy and competitive practices.
The move will help Google better tailor its ads to people's tastes. If someone watches a Major League Baseball clip online and lives in the Tampa Bay area, the firm could advertise Rays tickets in that person's Gmail account.
Consumers could also benefit, the company said. When someone is searching for the word "jaguar," Google would have a better idea of whether the person was interested in the animal or the car.
But, say consumer advocates, the new policy might upset people who never expected their information would be shared across so many different websites.
If you are a Google user, for instance, you may not want Google to use your social network to alert estranged friends, or your boss, that you are around the corner at a bar.
"Google's new privacy announcement is frustrating and a little frightening," said Common Sense Media chief executive James Steyer. "Even if the company believes that tracking users across all platforms improves their services, consumers should still have the option to opt out, especially the kids and teens who are avid users of YouTube, Gmail and Google Search."
Google can collect information about users when they activate an Android mobile phone, sign into their accounts online or enter search terms. It can also store cookies on people's computers to see which websites they visit or use its popular maps program to estimate their location.
Some analysts said Google's move is aimed squarely at Apple and Facebook, which have been successful in building unified ecosystems of products that capture people's attention. Google, in contrast, has adopted a more scattered approach, but an executive said in interviews that the company wants to create a much more seamless environment across its various offerings.
"If you're signed in, we may combine information you've provided from one service with information from other services," Alma Whitten, Google's director of privacy for product and engineering, wrote in a blog post.