Microsoft has filed an antitrust complaint against Google with European Union regulators, throwing its industry weight behind other companies that claim Google is not playing fair in capturing the lion's share of ad revenue from search.

Microsoft announced Wednesday that it launched a formal complaint against its rival, which accounts for more than 90% of the search market in Europe, placing Google way ahead of Microsoft's Bing search engine. In filing the complaint, Microsoft is joining its subsidiary Ciao, a price comparison site that has made similar accusations.

Google, which has yet to officially present its side, says it is in talks with EU regulators.

"We're not surprised that Microsoft has done this, since one of their subsidiaries was one of the original complainants," Google said in an emailed statement Thursday. "For our part, we continue to discuss the case with the European Commission and we're happy to explain to anyone how our business works."

Search is central to Google's advertising income, which accounts for most of the company's $30 billion in annual revenue. The EU embarked on a wide-ranging antitrust investigation of Google last November, triggered by complaints from much smaller search engines than Bing.

Microsoft's complaint takes the probe to another level and directs the EU's attention toward whether Google is denying a major rival access to key technologies necessary to index information on sites Google controls, such as YouTube, the world's largest video-sharing site. Microsoft claims Google has blocked Bing and Microsoft's Windows Phone 7, the company's mobile phone operating system, from properly accessing YouTube.

"Without proper access to YouTube, Bing and other search engines cannot stand with Google on an equal footing in returning search results with links to YouTube videos and that, of course, drives more users away from competitors and to Google," Brad Smith, senior VP and general counsel at Microsoft, said in a blog post announcing the complaint.

Microsoft also is accusing Google of preventing advertisers and online agencies from using third-party software to make the information they input into Google's Adwords easily accessible by other ad platforms, such as Microsoft's Adcenter. "If it's too expensive to port their advertising campaign data to competing advertising platforms, many won't do it," Smith says of advertisers. "Competing search engines are left with less relevant ads, and less revenue."

Microsoft recognizes that in filing the lawsuit, it is taking the same position other companies took against Microsoft in the Web browser market, leading to an antitrust ruling against the company in 2004. "There of course will be some who will point out the irony in today's filing," Smith says. If Google is found in violation of EU laws, it could be ordered to change its business model and to pay a fine equal to as much as 10% of the company's annual revenue, The New York Times reported.

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