Mozilla Thunderbird 2.0.0.9 has been found to contain a heap buffer overflow vulnerability due to the way it handles external-body MIME types. Systems running this version of Thunderbird are vulnerable to compromise or the execution of arbitrary code via specially crafted email messages. You should update to Thunderbird 2.0.0.12 as soon as possible.

Mozilla’s advisory is located at: http://www.mozilla.org/security/announce/2008/mfsa2008-12.html