Mozilla has released Thunderbird 17.0.3 and 17.0.3esr (Thunderbird for Organizations) on February 19, 2013. As a reminder starting with Thunderbird 17.0.2, Thunderbird is now following the branch numbering of Thunderbird 17.0esr instead of Firefox.
Besides security fixes this release also includes a fix for issues removing attachments via the keyboard while composing (Bug 799451). Depending on their update settings (Tools > Options… > Advanced > Update Tab), users will be prompted to update within in the next 48-hours. Users can also go to Help > About Thunderbird and click the Check for Updates button or go to getthunderbird.com and manually download and install Thunderbird. The next scheduled release will be Thunderbird 17.0.4 and 17.0.4esr on April 2nd, 2013.