Information about security issues fixes is available via these seven MFSAs (Mozilla Foundation Security Advisory):
http://www.mozilla.org/projects/securit ... hunderbird
It appears that there is no public Release Notes document released yet.
Secunia has assigned Highly Critical (4/5) advisory SA23420, link here.
UserAgent: Mozilla/5.0 (Windows; U; Windows NT 5.0; fi; rv:1.8.1) Gecko/20061010 Firefox/2.0


