nb1 writes:  

Java software allows you to run applications called "applets" that are written in the Java programming language. These applets allow you to play online games, chat with people around the world, calculate your mortgage interest, and view images in 3D. Corporations also use applets for intranet applications and e-business solutions.

Sun Microsystems has issued an update to fix stability and security problems with its Java software. It includes all operating systems. It is recommended that you update to the latest version. It's also necessary to remove the old java environments, not just update the new versions, as an attacker can target the old environments when they are still present.
Java Update 1.5.0_07