If you’re still running Mac OS X 10.4.x (“Tiger”), there’s no reason you shouldn’t feel as secure as a user running Mac OS X 10.5.7 with all its inherent updates. According to MacNN, Apple released Security Update 2009-002 for the previous operating system.
The update patches several areas of Tiger, including Apache, CoreGraphics, CUPS, Disk images, Flash Player plug-in, Help Viewer, Spotlight, X11, and more and fixes problems ranging from keeping PDFs opened in CoreGraphics from executing malicious code to preventing maliciously crafted Mach-O executables from causing the Finder to repeatedly terminate and relaunch.
There are four variants of the update (one each for Mac OS X 10.4.x on PowerPC and Intel-based hardware as well as two server versions) that can be located and installed via Mac OS X’s built-in Software Update feature.