Getting Silverlight version

Here is the post which gives you how to get the Silverlight version through Javascript.
http://www.kunal-chowdhury.com/2010/09/how-to-detect-installed-silverlight.html

If you want to get the Silverlight version inside Silverlight code you may invoke this function as follows.
http://silverlightedweb.blogspot.com/2008/05/silverlight-javascript-communication.html

Silverlight security aspects

The below link explains the security aspects of Silverlight. ie differences among the Transparent code,Safe critical code and Critical code along with the theory of user initiation.

http://msdn.microsoft.com/en-us/library/dd470128%28VS.95%29.aspx