Drupal 7.29 and Drupal 6.32, maintenance releases which contain fixes for security vulnerabilities, are now available for download. See the Drupal 7.29 and Drupal 6.32 release notes for further information.
Upgrading your existing Drupal 7 and 6 sites is strongly recommended. There are no new features or non-security-related bug fixes in these releases. For more information about the Drupal 7.x release series, consult the Drupal 7.0 release announcement. More information on the Drupal 6.x release series can be found in the Drupal 6.0 release announcement.
On February 13, 2008, Drupal 6 was released. The policy of the community is to support only the current and previous stable versions. (When Drupal 6 was released, Drupal 4.7.x was marked unsupported. When Drupal 7 came out, Drupal 5.x was marked unsupported.) This policy was created to prevent core and module maintainers from having to maintain more than 2 active major versions of Drupal.