Drupal 6 made its debut in February 2008. For eight years, it was supported, upgraded and patched. In February 2016, support for that version of the Drupal content management system finally lapsed. Drupal 6.38 was the last version released.
The Drupal development community encouraged admins and site owners to upgrade from Drupal 6. Without code support, any new security vulnerabilities would go unaddressed. Drupal 6 sites would miss out on cool new features, new modules and new themes (including responsive themes).