Use the following JavaScript to determine which .NET version is on a client PC:

<script language="JavaScript" type="text/javascript">var a = navigator.userAgent.match(/.NET CLR [0-9.]+/g);if (a == null)  document.write( ".NET Framework(s) is not installed" )else{  document.write( "The following versions of .NET Frameworks are installed:
" )  for (i = 0; i < a.length; ++i)  {     document.write( a[i] )     document.write( "
" )  }     }