Google's made a major change to its search algorithm, designed to deliver higher-quality results, which it says will noticeably affect nearly 12 percent of queries.
The move seems designed to weed out so-called 'content farms' which use search engine optimization techniques to push their sites to the top of the Google rankings. Many such sites have no original content at all - indeed, some stories have almost no content, consisting of just a couple of sentences. Nevertheless, they can perform well in searches.
"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," say Amit Singhal, Google fellow, and Matt Cutts, principal engineer.
"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."
While Google's algorithm is tweaked on a daily basis, most changes are more or less undetectable. This one, however, will see about one in eight queries affected.
The changes were heralded by an announcement from Google a month ago that it planned to try and cut down on the amount of spam in search results.
And last week it launched the Personal Blocklist Chrome extension, which lets users block sites which they've found to be useless.
Singhal and Cutts say that today's algorithm change does not rely on feedback from the Personal Blocklist - vitally important, as including that data would make it possible for people to game the results through yet more search engine optimization.
But, it says, the blocklist has proved a good way of checking whether the new algorithm is performing as planned.
"we did compare the Blocklist data we gathered with the sites identified by our algorithm, and we were very pleased that the preferences our users expressed by using the extension are well represented," they say.
"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."
Demand Media - widely regarded as just the sort of content fam Google is trying to eliminate - says it's not worried about 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," says
Larry Fitzgibbon, Demand's EVP of media and operations.
The changes hit the US today, with the rest of the world to follow over the coming weeks; and Google says there's more to come.