Here's a free lightweight tool that does it quickly - .NET Version detector 2007
If you want to do it manually, this page shows 4-5 good ways to do it. The MS Support page presents a method as simple as opening up the Framework folder and checking the versions installed (folder names)!
However, If you want to do it programmatically, the HttpBrowserCapabilities
class offers a GetClrVersions()
method that is accessible through the Request.Browser.GetClrVersions()
call. Of course, as others have mentioned, you can always query the Navigator.UserAgent property of the Browser too, via Javascript (I think this will show you the .NET versions only in IE):
javascript:alert(navigator.userAgent)