Google on Thursday announced a change to its search algorithm that reduces rankings for low-quality sites.
The changes, implemented in the last few days, impacts about 11.8 percent of Google's queries, Google's Amit Singhal and Matt Cutts wrote in a blog post. The duo defined low-quality sites as those that are a "low-value add for users, copy content from other websites or sites that are just not very useful."
"At the same time, it will provide better rankings for high-quality sites—sites with original content and information such as research, in-depth reports, thoughtful analysis and so on," they wrote.
Singhal and Cutts did not provide too many details about what this algorithmic change entailed; search engine ranking mechanisms are often closely guarded secrets. But they said this week's change did not rely on changes it received from its "Personal Blocklist" Chrome extension. That tool, introduced last week, lets Chrome users eliminate Google search results from dubious domains. Google did, however, compare the Blocklist data it has gathered with the sites identified by the algorithm, and found that user preferences are "well represented" in the new algorithm.
"If you take the top several dozen or so most-blocked domains from the Chrome extension, then this algorithmic change addresses 84 percent of them, which is strong independent confirmation of the user benefits," Singhal and Cutts wrote.
Google acknowledged that any change to its algorithm will affect the rankings of sites. "It has to be that some sites will go up and some will go down," they wrote. "It is important for high-quality sites to be rewarded, and that's exactly what this change does."
On that front, Demand Media said it saw "some content go up and some go down in Google search results" after the 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," Demand Media executive vice president of media and operations, Larry Fitzgibbon, wrote in a blog post.
In late January, Demand Media announced an initial public offering. Fitzgibbon said that while "we generally don't comment or speculate on changes by major search engines," Google's efforts were "top of mind for many people," so Demand Media decided to discuss it after coming out of the IPO quiet period.
Google makes "changes nearly daily in a quest to give consumers the best possible experience, as do we," Fitzgibbon wrote.
Google promised more updates that will improve the quality of page results in the months ahead. Today's change is launching in the U.S. at this point, but it will be rolled out elsewhere over time.
The news comes several weeks after Google accused Microsoft of copying Google results on Bing; an accusation Microsoft hotly denied. Earlier this year, Google also defended its search-related spam-fighting policies and denied that sites with Google ads get a free pass. It did, however, acknowledge an uptick in spam and pledged to crack down more heavily on content farms.
Editor's Note: This story was updated at 11am Eastern with comment from Demand Media.