Google search-results pages include the search terms in the URL, which gets passed along by Web browsers to the next page clicked.

Google has been targeted in a class-action lawsuit that accuses the company of violating user privacy by passing along search queries in referral links.

The suit, filed yesterday in U.S. District Court for the Northern District of California, argues that Google's practice of including search terms in the URL for search-results pages violates user privacy when that URL is passed onto the publisher of the Web site clicked on by a Google user. For example, when a Google user searches for "sushi restaurants in San Francisco," Google generates a search results page with a URL along the lines of "http://www.google.com/searchsourceid=chrome&ie=UTF-8&q=sushi+restaurants+in+san+francisco," and that URL gets passed along by your Web browser when you click on one of the results.

This is almost ubiquitous on the Web, as it allows Web publishers to see which sites are sending them traffic and which search terms are generating most of that traffic. However, Paloma Gaos, a resident of San Francisco, argued the practice allows third-party data mining companies to assemble a wealth of sensitive and personal information on searchers by aggregating their queries and linking them to personally identifying information, such as IP addresses or even their names should they do a vanity search coupled with another search term.

"Because Google's financial success depends on, among other things, the symbiotic relationship it shares with SEOs (search-engine optimization consultants) and the ability for third parties to engage in Web analytics, Google has placed a high priority on revealing individual user search queries to third parties," the plaintiffs argued in the complaint. The plaintiffs want the suit extended to include anyone who did a search on Google and clicked on a result after October 25, 2006.

Google did not immediately respond to a request for comment.

Search Engine Land's Greg Sterling and Danny Sullivan noted that the plaintiff is singling out Google for a practice followed by countless Web sites. Both Yahoo and Microsoft's Bing also include search terms in their search-results page URLs, and other Web pages can contain even more sensitive information within the URL that can be passed along by the browser when a user navigates to the next page.

While it's possible that search queries, names, and IP addresses could be linked, it would take no small amount of effort to capture enough queries to make it worth someone's time. AOL showed the world just how possible this was in 2006 by releasing a large amount of anonymized data that had enough specific query information to paint pictures of specific individuals.

Still, it's clear that should this practice be outlawed or discontinued, the world of Internet marketing would change drastically.

"Referrers are part of the reason that Internet marketing is so successful, because results are trackable. Without referrers, it becomes more like the offline world where people spend on marketing with relatively little (compared to the Internet) insight as to what works," Sullivan wrote in a blog post today.