Drupal 7.24 and Drupal 6.29, maintenance releases which contain fixes for security vulnerabilities, are now available for download. See the Drupal 7.24 and Drupal 6.29 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.
Drupal 7.24 and 6.29 were released in response to the discovery of security vulnerabilities. Details can be found in the official security advisory:
To fix the security problem, please upgrade to either Drupal 7.24 or Drupal 6.29.
For a while after the release, sites running certain versions of Drupal core may have seen an erroneous message from the Update Status or Update Manager module recommending that they update to Drupal 6.27 or Drupal 7.19, rather than the actual latest security release. This appears to be an issue related to the drupal.org Drupal 7 upgrade which has since been fixed; see this issue for further details.