Along with the 10.5.4 update, Apple has just released Security Update 2008-004 for users of Mac OS X Tiger (10.4). According to Apple, the update "is recommended for all [Mac OS X Tiger (10.4)] users and improves the security of Mac OS X." You can download this update for the following systems:
The update is available through Software Update (Apple menu > Software Update) or by downloading the installer packages by clicking the links above for your system. Apple has provided a support article for more details on this update.