Actually in the silverlight update it include the security and reliability improvements. And the update is the backword which is compatible with web applications built in previous versions of Silverlight. And for the more information on this you just click here (http://go.microsoft.com/fwlink/?LinkId=160518 ). But in this when I try to keep updating the itunes software so at that time I get the message that unable to install because another installation is running in the background. I am not getting this that how to fix this so if you have any suggestion on this so please help me as soon as it is possible for you.