By 2004, search engines had incorporated various undisclosed factors into their ranking algorithms to reduce the impact of link manipulation. Leading search engines Google, Bing, and Yahoo! have not disclosed the algorithms they use to rank web pages. Some SEO practitioners have researched different SEO approaches and shared their personal opinions. Patents related to search engines can provide information to better understand search engines.
In 2005, Google began providing personalized marketing list search results for each user. Google creates search results for logged-in users based on the user's previous search history.
In 2007,
On June 15, 2009, Google disclosed that they had taken steps to mitigate the effects of PageRank shaping by using nofollow attributes on links. Matt Cutts, a well-known Google software engineer, announced that Google Bot would no longer treat any no follow links in the same way to prevent SEO service providers from using nofollow for PageRank shaping. As a result of this change, the use of nofollow caused PageRank to evaporate. To avoid the above situation, SEO engineers developed alternative techniques to replace the nofollow tag with obfuscated JavaScript, thereby allowing PageRank shaping. In addition, several solutions have been proposed, including the use of iframes, Flash, and JavaScript.
In December 2009, Google announced that it would use all users' web search histories to populate search results.
On June 8, 2010, Google announced a new web indexing system called Google Caffeine. Designed to allow users to find news results, forum posts, and other content faster than before, Google Caffeine changes the way Google updates its index, making content appear on Google faster than before. According to Carrie Grimes, the software engineer who announced Google Caffeine, "Caffeine provides 50% more web search results than our previous index..."
Google Instant was launched in late 2010 with the goal of making search results more timely and relevant.
Historically, webmasters would spend months or even years optimizing their sites to improve search rankings. As social media sites and blogs grew in popularity, leading search engines made changes to their algorithms to enable fresh content to quickly rank in search results.