Drupal 6.1, a maintenance release that fixes problems reported using the bug tracking system, as well as security vulnerabilities is now available for download. The security issues identified were in code new to Drupal 6, and are therefore not applicable to sites running on Drupal 5.
Upgrading your existing Drupal 6 sites is strongly recommended. There are no new features in this release. For more information about the Drupal 6.x release series, consult the Drupal 6.0 release announcement.