By relying so much on factors such as keyword density which were exclusively within a webmaster's control, early search engines suffered from abuse and ranking manipulation. To provide better results to their users, search engines had to adapt to ensure their results pages showed the most relevant search results, rather than unrelated pages stuffed with numerous keywords by unscrupulous webmasters. This meant moving away from heavy reliance on term density to a more holistic process for scoring semantic signals. Since the success and popularity of a search engine is determined by its ability to produce the most relevant results to any given search, poor quality or irrelevant search results could lead users to find other search sources. Search engines responded by developing more complex ranking algorithms, taking into account additional factors that were more difficult for webmasters to manipulate. In 2005, an annual conference, AIRWeb (Adversarial Information Retrieval on the Web), was created to bring together practitioners and researchers concerned with search engine optimization and related topics.
Google used to make much of its ad hoc keyword search functionality available as well, but now the Keyword Planner is behind a paywall in AdWords as a premium feature. Difficulty scores are inspired by the way Google calculates its Competition Score metric in AdWords, though most vendors calculate difficulty using PA and DA numbers correlated with search engine positions, without AdWords data blended in at all. Search Volume is a different matter, and is almost always directly lifted from AdWords. Not to mention keyword suggestions and related keywords data, which in many tools come from Google's Suggest and Autocomplete application programming interfaces (APIs).