IE 11 and Browser detection

I have some ActiveX controls and other content on my website which prevents it from running properly on browsers others than Internet Explorer. Therefore I put a code for Browser detection. It looks like this:

private float getInternetExplorerVersion()
		{
			// Returns the version of Internet Explorer or a -1
			// (indicating the use of another browser).
			float rv = -1;
			System.Web.HttpBrowserCapabilities browser = Request.Browser;
			if (browser.Browser == "IE")
				rv = (float)(browser.MajorVersion + browser.MinorVersion);
			return rv;
		}

Therefore, I'm preventing users from accessing the site if the above function returns -1. However, one of the users recently installed IE 11 and reported that they cannot access the site. Does anyone knows how to modify the above code to let people with IE 11 in (but not people with other browsers)? It's a rather old site, using .NET 1.1 Framework.

Thanks in advance.