DuckDuckGo, a one-man-band search engine based out of Valley Forge, Pennsylvania, is aiming at Google's privacy practices with an unusual tactic: a billboard in San Francisco that proclaims "Google Tracks You. We Don't."

The ad, which cost DuckDuckGo founder and coder Gabriel Weinberg $7000 for four weeks, went up Thursday in San Francisco's tech-heavy SOMA district, along the highway dumping cars off the Bay Bridge into San Francisco. While the billboard is far from Google's Mountain View HQ, San Francisco is a Google-town, where many residents who work at the search giant board Wi-Fi enable, black executive shuttles for the daily commute to the Valley proper.

At issue is Google's habit of sending along a searcher's query to the site they are visiting, according to DuckDuckGo's founder and sole employee Gabriel Weinberg. So if you search on "athlete's foot" on Google, then click on a link, that site gets told that you searched on "athlete's foot." That's something that not many people know, Weinberg says, and something his search engine doesn't do.

Moreover, third-party ad tracking networks can also grab that info and add it to the store of information the companies store on users, Weinberg adds. It's not clear if any ad tracking networks actually do grab this information, since those companies are notoriously unforthcoming about what data they collect.

When talking about the idea, Weinberg built a quick website, donttrack.us, at the suggestion of friends, which took off earlier this month, and it's privacy message seemed to resonate with users. In fact, DuckDuckGo's traffic doubled after the site got attention on Hacker News and Stumbleupon and is now up to about 160,000 queries a day, which equates to about 5 million queries a month.

Weinberg chalks that success up to people not knowing that their search terms were available to marketers on search result pages.

"People know that Google is storing searches and they know about the employee snooping," Wienberg said. "The part many don't realize is that the serach term is being sent when the search is in the Google link."

Google takes issue with the claims made by donttrack.us, pointing out it is the only major search engine to offer HTTPS search, which hides referrer data.

"It’s unfortunate that DuckDuckGo is preying on people’s fears and offering incomplete information in order to garner attention," a company spokeswoman said in an e-mailed statement.

"For example, it is inaccurate to say that Google uses sensitive health-related terms to target ads on affiliated web pages.

"All search engines and websites use referrer terms as part of the architecture of the web, but we recognize our responsibility to protect the data that users entrust to us and we give them meaningful choices to protect their privacy."

While that's a pittance compared to the billions served daily by Google, but many of DuckDuckGo's users are alpha geeks, much as Google was adopted by the tech set back in the late 1990s. Weinberg powers his search engine using his own web crawler, results from Bing, and APIs from a number of companies, including the mathematical answer engine WolframAlpha.

DuckDuckGo, along with the new, well-funded start-up Blekko, have also been challenging Google on relevance, focusing on removing many spam and low-quality content farms from their results. That approach is resonating, as tech observers have begun to turn on Google for the number of low-quality sites that show up in search results. That's thanks to search optimization methods used by sites to lure searchers, even if a webpage lacks any quality content.

Weinberg's search engine avoids the problem of referrers – the habit of web browsers telling a new webpage what page you just came from – by doing a quick redirect any time you click on a link in DuckDuckGo. Like Google, DuckDuckGo also offers an HTTPS version of its search engine, which naturally only passes the top-level domain you are coming from (e.g. https://google.com), instead of passing the entire url along (e.g. http://www.google.com/#sclient=psy&hl=en&q=what+I'm+searching+for).

Weinberg's not the first to raise the question. Christopher Soghoian, an independent privacy activist who has worked at the FTC and been a Google intern Fellow, filed an FTC complaint in October last year, alleging Google is violating its privacy promises to users by passing along the queries.

Google itself briefly turned off referrers when it moved to AJAX search, and its HTTPS site, but faced a backlash from online marketers who live and breathe by where they rank in Google searches.

Matt Cutts, Google's public face for webmasters, defended Google's policy in a thread on Hacker News, saying the company cares about privacy and users can always try their HTTPS search. As for why the search giant won't stop sending referrers, Cutts explained, "When Google switched to AJAX-based search, that temporarily stopped sending referrers, and lots of people screamed bloody murder."

But Weinberg counters that there are other ways for websites to get the data they want without being able to tie it to a particular user using Google's Webmaster tools, rather than relying on analytics tracking scripts installed on their own website.

"It will tell which terms you are getting traffic from, and how you rank for that term," Weinberg says. "You can get that info if you need it, so you almost don't need them to send it."

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