Web search engines looked at more than just keywords but also how many links each site got from other sites. (Links that link back to other sites are referred to as “backlinks.”) For instance, in the Google search engine, when users looked for “clothes for dogs,” Google would see which sites contained that phrase, and then, Google would look at how many other websites linked to each of those pages, to measure how well-liked and popular they were. The “clothes for dogs” sites that had the most backlinks were considered to be the most popular, and thus, the best websites on the internet about “clothes for dogs.” Therefore, Google ranked them the highest because people would not post links to “clothes for dogs” sites that they thought were lacking.

Backlinks grew more and more in power. Webmasters had previously realized that if 10 keywords were good, then 10 thousand keywords were better, they realized that having many backlinks was better than a few. However, they cannot force other sites to link to them, so they quickly build many other sites that are useless and purposeless to link those sites to their main website. Search engines had no way to know who owned what websites, nor could they recognize when sites have been created for the sole purpose of making other sites look good. Thus whoever created the largest number of backlink sites would have the greatest amount of power.

Some people use this mechanism to sell services as paid by making a bunch of purposeless sites for the sole purpose of hosting links to other sites instead of making useful sites by themselves. Thus, hiring an SEO company that guarantees hundreds or thousands of backlinks to help you boost your popularity means hiring one of those people with their legions of zombie link farms and automatically letting you enter into link exchange programs.