See the Tiki Release Notes (http://tiki.org/ReleaseNotes92) for complete information.
The 6.8 update includes the security patch only. Thank you Egidio Romano (aka EgiX) for reporting this security vulnerability (which is in 9.2 as well)
The Tiki 9.x series is a Long Term Support (LTS) version, and will be supported until November 2015 (or upon the release of Tiki 16). Tiki admins are highly encouraged to upgrade to this latest version as the 8.x series is now end-of-life (EOL) and is no longer supported. The Tiki 6.x series remains LTS through 2014. Refer to the Tiki Version Lifecycle (http://tiki.org/Version+Lifecycle) for details.
Meanwhile, the Tiki Community continues to work on the next generation of Tiki Wiki CMS Groupware: Tiki 10, which will be available later this year.
To download Tiki 9.2 LTS, 6.8 LTS, or any Tiki release, visit the Tiki download page at http://tiki.org/Download.