Those of you using Mozilla Thunderbird in the 1.5.x branch should head on over to our
Downloads section and get the latest update. Mozilla has
updated Thunderbird to 1.5.0.12, including some important security updates that have
been detailed on their bug list.
A better idea in the long run, of course, is to update your client to the new 2.0 branch, which you can
download here. The 1.5.x branch will still receive security updates and support for a while yet, but eventually they will drop support for it along with the 1.5.x branch of Firefox.