Algorithms have been called “black boxes”, because the factors used by the leading websites in their algorithms are typically proprietary information which is not released to the public. While a number of search engine optimization (SEO) firms offer the services of attempting to increase the ranking of a client's web content or website, these SEO firms do not typically know the exact algorithms used by Google and Facebook. Web crawlers can only access 26% of new online content "...by recrawling a constant fraction of the entire web".
