As of March 30, 2010, the current version of Sun's Java client is Java(TM) 6 Update 18.
If you see the Java Update icon or "Java Update Available" balloon in the lower right corner of the screen, the latest version of Java should be ready to install. You can click the icon and follow its prompts to apply the update.
Note: We recommend that you do not install any offered "extras" like Microsoft's Bing Toolbar, MSN Toolbar, or OpenOffice.org Installer. Please un-check these options if they appear.
Or, our How To Update Sun's Java Software has complete steps on how to install Java from either the "Java Update Available" message or how to download and install Java manually .
This release DOES contain fixes for security vulnerabilities. It also added seven new root certificates, removed three root certificates and five root certificates replaced with stronger signature algorithms from VeriSign, Thawte and GeoTrust. The full list of changes may be found here: http://java.sun.com/javase/6/webnotes/6u19.html