MOUNTAIN VIEW, California: Google, the online search giant, has launched a behavioural advertising system that will target ads at users based on their browsing history, but which will also allow consumers to view and edit the information collected about them, and opt out of the scheme.

While Yahoo and Microsoft currently run similar programmes, it has been argued that Google's size and influence on the online ad market mean its innovations often have a greater impact.

The company will now track the websites consumers visit and which also use its AdSense programme, and then show web users ads related to the type of content they are interested in, whether or not they are viewing a portal related to that specific topic.

As well as enabling advertisers to reach their target audience more effectively, Google argues publishers will benefit from increased revenues and consumers will gain by seeing ads which are relevant to them.

It has identified 20 "categories" of user interest, and a further 600 "subcategories", though these do not include "sensitive" information such as race, religion or health and financial matters.

While Google will not directly inform users their behaviour is being monitored, it will display a link on pages displaying targeted ads to a website providing information about the new service.

This site will also allow consumers to view and edit information relevant to their online activity, and to opt out of receiving "interest-based advertising".

However, Ari Schwartz, coo of the Center for Democracy and Technology, said that "more needs to be done on how to educate people and tell them how to opt out."

Some publishers are also said to be wary about giving Google access to information about their users which will then be used to place ads on other portals, particularly given the massive advertising reach of the search provider.

Data sourced from New York Times; additional content by WARC staff