Page "Search engine optimization" Paragraph 8

By 2004, search engines had incorporated a wide range of undisclosed factors in their ranking algorithms to reduce the impact of link manipulation.

Google says it ranks sites using more than 200 different signals.

The leading search engines, Google, Bing, and Yahoo, do not disclose the algorithms they use to rank pages.

SEO service providers, such as Rand Fishkin, Barry Schwartz, Aaron Wall and Jill Whalen, have studied different approaches to search engine optimization, and have published their opinions in online forums and blogs.

SEO practitioners may also study patents held by various search engines to gain insight into the algorithms.