1) system loads increase by 3x magnitude
2) system starts to work slowly
3) the JVM has now loaded
4) the virus starts to install...
you can use the 15 minutes it takes java to load a virus (or anything) to close your web browser at this point.
5) If you are not able to stop the virus, look out for strange windows with dodgy toolkits. Yes, Java AWT, this means you.