Although the search giant hasn't officially acknowledged it, reports indicate that the move is primarily targeted at "content farm" sites.
Google engineers Amit Singhal and Matt Cutts defined low-quality sites in a blog as those that are a "low-value add for users, copy content from other websites or sites that are just not very useful."
The duo said, "We believe it's a big step in the right direction of helping people find ever higher quality in our results. We've been tackling these issues for more than a year, and working on this specific change for the past few months. And we're working on many more updates that we believe will substantially improve the quality of the pages in our results.
"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.”
Google did not provide many details about the algorithmic search ranking change but reportedly said it did not rely on changes it received from its "Personal Blocklist" Chrome extension.
Chrome, released last week, allows users to eliminate Google search results from dubious domains. Google did say that it compared 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 site rankings will be affected by the change to its algorithm.
"It has to be that some sites will go up and some will go down. It is important for high-quality sites to be rewarded, and that's exactly what this change does," the Google pair said.
Google also promised to implement the changes elsewhere in the coming months.
