IT:AD:HTTP_USER_AGENT

Examples are:

Mozilla/4.7 [en] (WinNT; U)

Mozilla/5.0 (Windows NT 6.1; rv: 12.0) Gecko/20100101 Firefox/12.0

This is then used by IIS to determine it's capabilities and can be retrieved from the: http://msdn.microsoft.com/en-US/library/system.web.httpbrowsercapabilities

• http://stephenwalther.com/archive/2010/03/05/use-asp-net-4-browser-definitions-with-asp-net-3-5.aspx