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TrustRank

　　TrustRank is a link analysis technique described in a paper by Stanford University and Yahoo! researchers for semi-automatically separating useful webpages from spam. In an attempt to combat Spam, the leading search engines introduced a system of assessing trust. Analysis took place which centred on identifying 'hub sites' which were leaders in their particular field and these became trusted domains. Domains which received links from these trusted sources then gained trust for themselves to the benefit of their search engine ranking. It is believed that Google and Yahoo have implemented trust based ranking algorithm. Examples of trusted hub sites might be .gov, .edu domains as well as leading web portals and information sources.

　　Many Web spam pages are created only with the intention of misleading search engines. These pages, chiefly created for commercial reasons, use various techniques to achieve higher-than-deserved rankings on the search engines' result pages. While human experts can easily identify spam, it is too expensive to manually evaluate a large number of pages.

　　TrustRank method calls for selecting a small set of seed pages to be evaluated by an expert. Once the reputable seed pages are manually identified, a crawl extending outward from the seed set seeks out similarly reliable and trustworthy pages. TrustRank's reliability diminishes as documents become further removed from the seed set.

　　The researchers who proposed the TrustRank methodology have continued to refine their work by evaluating related topics, such as measuring spam mass.