Some people are annoyed when this pop-up appears on their screen, and wonder if it is legitimate or necessary:
This is indeed a legitimate software update from Sun Microsystems, the vendor that provides Java. Java is a programming language and runtime environment used by a number of websites to display interactive web content. In order to secure your computer from online threats, you should keep all of your online software up-to-date. This includes Java. So, the next time this pop-up happens, you should click on the pop-up window and allow the update to proceed. It should only take a few minutes.