Answer - What is Machine.config? Machine configuration file: The machine.config file contains settings that apply to the entire computer. This file is located in the %runtime install path%Config directory. There is only one machine.config file on a computer. The Machine.Config file found in the "CONFIG" subfolder of your .NET Framework install directory (c:WINNTMicrosoft.NETFramework{Version Number} CONFIG on Windows 2000 installations). The machine.config, which can be found in the directory $WINDIR$Microsoft.NETFrameworkv1.0.3705CONFIG, is an XML-formatted configuration file that specifies configuration options for the machine. This file contains, among many other XML elements, a browser Caps element. Inside this element are a number of other elements that specify parse rules for the various User-Agents, and what properties each of these parsing supports. For example, to determine what platform is used, a filter element is used that specifies how to set the platform property based on what platform name is found in the User-Agent string. Specifically, the machine.config file contains: platform=Win95 platform=Win98 platform=WinNT ... That is, if in the User-Agent string the string "Windows 95" or "Win95" is found, the platform property is set to Win95. There are a number of filter elements in the browserCaps element in the machine.config file that define the various properties for various User-Agent strings. Hence, when using the Request.Browser property to determine a user's browser features, the user's agent string is matched up to particular properties in the machine.config file. The ability for being able to detect a user's browser's capabilities, then, is based upon the honesty in the browser's sent User-Agent string. For example, Opera can be easily configured to send a User-Agent string that makes it appear as if it's IE 5.5. In this case from the Web server's perspective (and, hence, from your ASP.NET Web page's perspective), the user is visiting using IE 5.5, even though, in actuality, he is using Opera.