.Net Configurations-Application level,Machine level,Security Level

Application Configuration File:This configuration file is used to set the settings for single application.It is application level configuration file.Any changes made to application configuration file will applicable to only single application.

Machine Configuration : This configuration file is used to set the settings for a resource that is used by multiple applications.The machine.config file is located in C:\\Microsoft.NET\Framework\\config\machine.config.This is a system level configuration file.Any changes made to this file will applicable for all applications that are located in that system
Security Configuration File:
Security configuration files contain information about the code group hierarchy and permission sets associated with a policy level. It is strongly recommended that you use the .NET Framework Configuration tool (Mscorcfg.msc) or Code Access Security Policy tool (Caspol.exe) to modify security policy to ensure that policy changes do not corrupt the security configuration files.