Starting today, online ads shown across Google's network of partner websites and on its video-sharing site YouTube are based on the user's browsing history.

Joining an industry trend that has raised privacy concerns, the company introduced a new program called "interest-based" advertising, hoping to make ads more relevant and useful for web surfers and more profitable for it and its advertising partners.

Avoiding the use of a more controversial notion like "behavioral advertising," the new ad system announced Wednesday on Google's official blog and its public policy blog, will let web surfers pick categories of interest and then associate those interests with the browser. The ads will associate categories of interest — say sports, gardening, cars, pets — with the browser, based on the types of sites the user visited and viewed.

So far, Google has shown ads based mainly on what a user's interests are at a specific moment. For example, if someone would have searched for [digital camera] on Google, they got ads related to digital cameras. If they would have visited the website of one of Google's AdSense partners, they were shown ads based on the content of the page.

"For example, if you're reading a sports page on a newspaper website, we might show ads for running shoes," Google's VP of Product Management Susan Wojcicki wrote on the official Google blog, adding that in certain situations one keyword or the content of a web page is simply not enough information to serve highly relevant ads.

Advertisers have long been asking for a way to behaviorally target ads but the company insisted the new "interest-based" system will benefit end-users by showing them ads they're genuinely interested in. "We believe there is real value to seeing ads about the things that interest you," she added.

Google privacy officials, as recently as early 2008, said they had no plans to engage in "behavioral advertising," which according to the company officials, is not very effective.  

"Behavioral advertising" has been a topic of interest at the Federal Trade Commission since at least 2006, when the consumer protection agency began holding hearings about how online technology raised consumer privacy issues.

Before launching the behavioral advertising beta, Google said they solicited advice from several groups including users, "privacy advocates" and even government experts.

The company refused to use the term "behavioral advertising" calling it "a vague term" that "often gets lumped in with questionable practices," Christine Chen, a Google spokeswoman said. "Google is specifically offering the ability for advertisers to reach users who previously visited their own sites, and to reach users by the interests as determined by Google or selected by users in the Ads Preferences Manager."

Trying to make their way around potential criticism, Google also set up an Ad Preferences manager that allows users to add their own interests manually and opt out of certain categories. It also offers an "opt-out" cookie that users can embed in their browsers to keep interests from being tracked at all, and a browser plug-in that accomplishes the same thing.