Mozilla has released Thunderbird 3.1.7 and Thunderbird 3.0.11, each of which fixes a number of critical security issues including potential buffer overflows. Two versions of the update are available depending upon the version of Thunderbird installed. All Thunderbird 3.1 and 3.0 users should apply the update as soon as possible.
Note that this release of Thunderbird 3.0 will be the final release. Thunderbird 3.0 users are encouraged to upgrade to Thunderbird 3.1. For more information, see http://www.mozillamessaging.com/en-US/about/press/archive/2010-10-19-01