Google Inc made substantial changes to its search engine in a direct attack on companies that churn out low-quality stories and videos.

The results of the improvements to Google's algorithms used to list search rankings over the past few days affected nearly 12 percent of searches, Google said in a blog post on Thursday.

Google launched the clean-up after users urged stronger action against so-called content farms, which rely on armies of low-paid freelancers to crank out stories and videos designed to appear higher on search engine results.

This update is designed to reduce rankings for low-quality sites -- sites which are low-value add for users, copy content from other websites or sites that are just not very useful, Google fellow Amit Singhal and principal engineer Matt Cutts wrote in the blog post.

At the same time, it will provide better rankings for high-quality sites with original content and information such as research, in-depth reports, thoughtful analysis and so on.

While Google did not cite companies it regards as content farms, the tag is often pinned to Demand Media, Yahoo Inc's Associated Content, and AOL's Seed, which publish stories on such topics as how to make a paper lantern or five ways to sooth dry skin.

A major slice of content farms' revenue is generated through search engines. Demand Media, for instance, said 28 percent of its revenue came from Google in the first nine months of 2010.

As might be expected, a content library as diverse as ours saw some content go up and some go down in Google search results, Larry Fitzgibbon, Demand Media executive vice president of media and operations, wrote in a blog post on Thursday in response to the Google changes.

It's impossible to speculate how these or any changes made by Google impact any online business in the long term but at this point in time, we haven't seen a material net impact on our Content & Media business.

Shares of Demand Media, which debuted as a public company in January, fell 1.6 percent to close at $22.96 on the New York Stock Exchange. The company's initial public offering was priced at $17 in January.

Google has been cracking down on others, including retailer J.C. Penney, according to a New York Times report, that try and game Google algorithms to place high in search results.

(Reporting by Jennifer Saba; Editing by Richard Chang)

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