Users of Mac OS X and specifically the Safari browser may have noticed that Java-based browser applets such as the tree viewer in the IMDI browser and LAMUS currently do not get displayed in the browser window. In addition, the web start versions of applications such as ELAN, ARBIL and KinOath may not launch temporarily. This is due to a security update issued by Apple on 31 January, as can be read in an article on thinkdigit.com:
Apple has blocked the Java web plugin from running on Mac OS X computers under its Xprotect security system, citing security concerns. The Xprotect system built into Mac OS X requires applications to be a certain version to ensure that all applications are properly updated to remove security loopholes. However, Apple has updated Xprotect to require the JRE version 1.7.0_11-b22 build of Java whereas the current Java build released by Oracle is JRE version 1.7.0_11-b21.
This means that applets will not be functioning until the mentioned upcoming version of the Java Runtime Environment (JRE) gets released. You can test whether your system is affected either by trying to use one of the above mentioned tools or browsing to Oracle’s Java test page.
If the browser you are using is affected by this update, you may want to consider using Firefox instead, as that browser seems least affected. There are instructions on how to enable applets in Firefox should this not work straight away.
Web start may be broken as a result of the security update but rebooting your computer should resolve this.