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That banner ad you see today on a Yahoo Web page may have been triggered by a search you did on the company's search engine two days ago.

That is because Yahoo tracks users' queries on its search engine and, based on that information, tailors the graphical ads it beams at them later throughout its network of sites, a Yahoo official said Thursday.

In this advertising program, called Yahoo Impulse, Yahoo captures a user's query terms and categorizes them. For example, a user who searches for the term "credit card" will be tagged as someone who is interested in the broader "financial services" category, said Usama Fayyad, senior vice president and chief data officer at Yahoo.

Then that user will be served graphical ads, such as banner ads, from participating advertisers in that financial services category while he is in the network of Yahoo sites, Fayyad said.

The program is a sort of twist and extension of search-based advertising, which traditionally has involved providing a set of text ads along with the list of search results based on a user's query.

But unlike with paid search programs, which target text ads to users on a one-time basis and only within the search results pages, Yahoo Impulse takes note of a user's queries to determine what kinds of graphical ads he will see elsewhere on Yahoo over a period of time.

You Said It Was OK

Yahoo Impulse tracks queries through users' Yahoo cookies and serves up the subsequent graphical ads for 48 hours afterward, a company spokeswoman said. Yahoo Impulse has existed for about four years, but ads previously were triggered for only a 1-hour period after the user's search session, she said.

This particular incarnation of Yahoo Impulse, with the much longer 48-hour ad tailoring period, was launched about three months ago, she said. Advertisers sign up for the program, but it's not an opt-in program for users, she said.

This means that users aren't asked for their permission to have ads tailored to them based on their search queries. However, the spokeswoman pointed out that this type of ad-customization activity is noted in Yahoo's privacy policy.

In fact, Yahoo's privacy policy states that the company "automatically receives and records information on our server logs from your browser, including your IP address, Yahoo cookie information, and the page you request. Yahoo uses information for the following general purposes: to customize the advertising and content you see, fulfill your requests for products and services, improve our services, contact you, conduct research, and provide anonymous reporting for internal and external clients."