Current technology: Search engines consider many signals

To reduce the impact of link schemes, search engines have developed a wider range of undisclosed off-site factors they use in their algorithms. As a search engine may use hundreds of factors in ranking the listings on its SERPs, the factors themselves and the weight each carries can change continually, and algorithms can differ widely. The four leading search engines, Google, Yahoo, Microsoft and Ask.com, do not disclose the algorithms they use to rank pages. Some SEOs have carried out controlled experiments to gauge the effects of different approaches to search optimization, and share results through online forums and blogs. SEO practitioners may also study patents held by various search engines to gain insight into the algorithms.