The updates, which are available for Mac OS X 10.6.8 Snow Leopard and 10.7.3 Lion (including both OS’s Server editions), patch multiple vulnerabilities in Java 1.6.0_29—including some that could allow malicious code to run on your Mac outside of the Java sandbox, triggered merely by your visiting a webpage containing the right nefarious code.
For full details on the update, Apple points
The update patches no fewer than a dozen vulnerabilities, including the one exploited most recently in the newly-discovered Flashback Trojan horse variant.
The security holes in question were patched for Windows users back in February;
Apple has long been criticized for lagging behind Windows in such areas.