You can use the UserName property to identify the user on the current thread, to the system and application for security or access purposes. It can also be used to customize a particular application for each user.

The domain account credentials for a user are formatted as the user's domain name, the '\' character, and user name. Use the UserDomainName property to obtain the user's domain name and the UserName property to obtain the user name. A user name is typically an abbreviated combination of the user's first and last names.

The following example displays the user name of the person who started the current thread.

' Sample for the Environment.UserName property
Imports System

Class Sample
   Public Shared Sub Main()
      Console.WriteLine()
      '  <-- Keep this information secure! -->
      Console.WriteLine("UserName: {0}", Environment.UserName)
   End Sub 'Main
End Class

// Sample for the Environment.UserName property
using System;

class Sample
{
    public static void Main()
    {
    Console.WriteLine();
//  <-- Keep this information secure! -->
    Console.WriteLine("UserName: {0}", Environment.UserName);
    }
}

// Sample for the Environment::UserName property
using namespace System;
int main()
{
   Console::WriteLine();

   //  <-- Keep this information secure! -->
   Console::WriteLine( "UserName: {0}", Environment::UserName );
}

.NET Framework

.NET Framework Client Profile

• EnvironmentPermission 

  for read access to the USERNAME environment variable. Associated enumeration: EnvironmentPermissionAccess..::.Read

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

Reference