Apple has released Java Update 5 for Mac OS X 10.5 to address assorted security vulnerabilities. Essentially this upgrades Java 1.6.0_13 to 1.6.0_15, Java 1.5.0_19 to 1.5.0_20, Java 1.4.2_21 ton 1.4.2_22, and fixes an apparently Mac-specific bug in Java Web Start command launcher. Check Software Update to download.