Behavioural advertising systems such as the internet service provider (ISP) traffic-intercepting system proposed by Phorm have run into controversy over the degree to which people were informed about and able to opt out of the system.
Google's system initially will work only on its YouTube video sharing site and on websites which use its AdSense technology to choose and display ads. Searches at Google.com will not be affected during the pilot phase.
Google said that it recognised that tracking systems raise privacy concerns and that it was "committed to transparency and user choice".
"We already clearly label most of the ads provided by Google on the AdSense partner network and on YouTube," said Susan Wojcicki, Google product manager, in a posting on Google's blog. "You can click on the labels to get more information about how we serve ads, and the information we use to show you ads. This year we will expand the range of ad formats and publishers that display labels that provide a way to learn more and make choices about Google's ad serving."
Google's system will differ from others by allowing users to edit the list of interests that Google creates by observing people's web surfing, adding or removing categories of interest.
"While interest-based advertising can infer your interest in adventure travel from the websites you visit, you can also choose your favourite categories, or tell us which categories you don't want to see ads for," said Wojcicki. "Interest-based advertising also helps advertisers tailor ads for you based on your previous interactions with them, such as visits to their websites."
Behavioural systems are popular with advertisers because they reduce wasteful spending on people who would never be interested even in a particular category of products never mind their own product.
They are popular with web publishers because the systems bring in advertisers and ensure an income stream.
"By making ads more relevant, and improving the connection between advertisers and our users, we can create more value for everyone," said Wojcicki. "Users get more useful ads, and these more relevant ads generate higher returns for advertisers and publishers. Advertising is the lifeblood of the digital economy: it helps support the content and services we all enjoy for free online today, including much of our news, search, email, video and social networks."
Google said that users will be able to opt out of the service altogether, and that it has designed a plug-in for browsers that means that the opt-out will survive any deletion of cookie files.
The Internet Advertising Bureau (IAB) last week published guidelines for behavioural advertising with Google as one of the signatories to the principles it established.
"The Good Practice Principles set out commitments to transparency, user choice and education. The Principles complement current UK data protection laws with new practices relating to the collection and use of online data," said an IAB statement.
The first principle of the guidelines (8-page / 113KB PDF)states: "Each Member shall provide clear and unambiguous notice to users that it collects data for the purposes of [online behavioural advertising]."
Google said that users could find out about the tracking at its Privacy Center; from clicking on the 'ads by Google' notice on ads themselves; and at its Ad Preferences Manager, though it is not clear how users will be informed of the practice in the first place.