Google has updated sitelinks, the column of sub-links beneath a Google search result that allows navigation straight to pages within a main site. The update makes sitelinks more visible, gives them flexible rankings based on the particular search query, increases the maximum number from eight to 12, and establishes a clearer hierarchy for the domains of search results.
Under the hood, the update also improves the quality of sitelink results. The signals Google uses specifically to generate and rank sitelinks, such as the link structure of a site, are now combined with the overall ranking algorithm, so main search results and sitelinks are now ranked and displayed based on one unified set of principles. – Google Improves Visibility and Rankings for Sitelinks (ReadWriteWeb)