If you recently run a windows update check, you may realise there's a new component to update, that is Microsoft Silverlight. If you are not sure, go to control panel and click on add/remove icon and see whether Microsoft Silverlight is in the program list or not? If you don't see it in the program list, run windows update now or click here.
What is Microsoft Silverlight?
"Microsoft Silverlight is a cross-browser, cross-platform plug-in for delivering the next generation of .NET based media experiences and rich interactive applications for the Web. Silverlight offers a flexible programming model that supports AJAX, VB, C#, Python, and Ruby, and integrates with existing Web applications. Silverlight supports fast, cost-effective delivery of high-quality video to all major browsers running on the Mac OS or Windows"
If you have installed Silverlight, some rich-content websites you visit will request you to enable silverlight application. Microsoft created Silverlight to enable developers to build rich multimedia interactive web contents within that platform. There will more applications build within Silverlight coming soon.
Click here for more info on Microsoft Silverlight.
