On Thursday, Apple’s Software Update mechanism sprang to life with a Java update for both Snow Leopard and Leopard users. So what’s new?

The updates bring with them the usual security fixes for Java’s venerable cross-platform technology. A full list of changes included in the update are available on Apple’s website for both Snow Leopard and Leopard, according to MacUser.

The two updates, Java for Mac OS X 10.6 Update 1 and Java for Mac OS X 10.5 Update 6, are also available for download directly from Apple’s website. The Leopard update requires 10.5.8 and is a 122 MB download, while the Snow Leopard version requires 10.6.2 and comes in at a svelte 78 MB.

What the updates share in common are fixes for vulnerabilities in Java 1.6.0_15, as well as patching Java 1.5.0_20. One such vulnerability allows an untrusted Java applet to obtain elevated privileges, which could enable it to then do something unpleasant. Both updates fix a loophole in which an expired certificate for an applet could be regarded as valid.

The updates are available now via Software Update or from Apple’s Support downloads page, and both require a system restart after installation.