What is "Silverlight"?
Microsoft Silverlight is an application framework for writing and running browser plug-ins or other rich internet applications, with features and purposes similar to those of Adobe Flash. The run-time environment for Silverlight is available as a plug-in for most web browsers. While early versions of Silverlight focused on streaming media, current versions support multimedia, graphics and animation, and give developers support for CLI languages and development tools.Do I need Silverlight?
No, at least not yet. Microsoft would like to replace Adobe Flash with it's "Silverlight"… but that's unlikely.There are only a few websites that use Silverlight; You won't miss something in the web when not having it installed.
Silverlight gets also installed by using Windows-Update.
Silverlight & Privacy
Similar to Flash, Java and other plugins, Silverlight may also be a security risk. It can reveal your real IP-address when using a proxy service (IP:Port proxy or web-proxy). The reason for this is that a usual proxy works only within your browser; but plugins and add-ons work like independent applications, so your proxy may get ignored by them. Better turn off plugins/addons that you don't really need.Silverlight official Website: http://www.silverlight.net/