 There has been considerable speculation as to why this is the case, but we briefly examine two reasons that have been prominent in discussions in the literature: (a) the interests of advertisers who sponsor search engines; and (b) schemes used by technically-savvy individuals and organizations to manipulate the ordered ranking of sites returned by search engines. (A third reason that is also sometimes suggested has to do with the nature of the algorithms used by major search engine companies; that issue is examined in this Section 3.1.3).