Google (GOOG) has adjusted its search-engine ranking system to demote what it considers "low quality" sites and boost sites with original content and substantial analysis.
The rejiggering of its listings will affect about 12% of user queries, the company posted on its blog Thursday. The changes currently impact only U.S. pages, but the system will be rolled out globally "over time," Google says.
"Google depends on the high-quality content created by wonderful websites around the world, and we do have a responsibility to encourage a healthy Web ecosystem," according to the blog post. "Therefore, it is important for high-quality sites to be rewarded, and that's exactly what this change does."
Last month, Google was in a dead heat with Yahoo (YHOO) for ownership of the most popular U.S. Web properties, with both companies' sites attracting roughly 179 million unique users each, according to ComScore. Microsoft (MSFT), came in at No. 3, with sites attracting about 177 million unique users in January.