Google and Microsoft appear to have been flooding their smaller search engine rivals with spam ads, to limit the number of higher-value ads that appear on them, according to data viewed by POLITICO.

Ads are considered “spam” if they appear in search results but have little to no relevance to the search terms a user has entered, and may direct users to less reputable sources. Such ads generate little value to search engines overall.

Pushing spammy ads to their smaller partners tilts the scales in favour of the bigger search engines in two ways. Firstly, it limits how much money smaller search engines can make, and gives Google and Microsoft a greater share of the more profitable ads. Secondly, users of alternative search engines like DuckDuckGo may be turned off by the poor ad choices when they search. This could encourage them to use Google and Bing instead, if they think those sites offer better and more reliable ads.

POLITICO reports that the findings come from data compiled by adtech researchers who wish to remain anonymous for fear of damaging their relationship with either Google or Bing.

Smaller search engines rely on the results of Google and Microsoft—so-called “gatekeeper search engines”—as they have the lion’s share of the search market. Google, of course, has by far the biggest share, with 90 percent, and up to 600 billion websites indexed. On the other hand, Bing has a 7 percent share but indexes more or less 150 billion web pages. POLITICO explains that these alternative search engines often have agreements with Google or Microsoft. This means that these two companies also supply the ads that appear on top of search result pages.

Readers may be surprised to discover that the privacy-focussed search engine DuckDuckGo uses Microsoft for its ads. According to DuckDuckGo “…your searches cannot be tied back to you”, however, that protection stops when you click on an ad: “When you leave our site, you are subject to other sites’ policies, including their data collection practices. For ads from Microsoft, you also pass through Microsoft Advertising’s platform.”

In its article, POLITCO compares the ads shown by DuckDuckGo and Bing for the search term “depression”, with DuckDuckGo showing obviously lower-quality ads. Search ads are subject to all kinds of factors so we thought we’d try it ourselves. We saw the same result.

DuckDuckGo ads for "depression"
Microsoft ads for the search “depression” on DuckDuckGo
Bing ads for "depression"
Microsoft ads for the search “depression” on DuckDuckGo

According to Marc-André Rousseau, a lawyer at the German law firm Schalast, the findings are in parallel with the Google Shopping saga as Google, once again, has conducted self-preferencing practices.

A spokesperson from Google told POLITICO that all ads signed up to search engine partners can appear on both Google’s and partner’s search results; however, the company “has certain algorithms in place that put controls on the types of ads shown.”

On the other hand, alternative search engines have reacted differently to the findings. DuckDuckGo said that it’s “constantly working to improve the quality of its results.” Qwant, a search engine that relies on Microsoft’s indexes, has started to study the advertising area in more detail in recent months. Startpage, a privacy search engine like Qwant, admits to using Google Ad Network for its ads but argues that the low-quality ads result from less user tracking. POLITICO, however, dispels this as the same ads appear on new machines that never used Bing or Google when they conducted their experiment.