Obsolete Attribute

The Obsolete attribute marks a program entity as one that is no longer recommended for use. Each use of an entity marked obsolete will subsequently generate a warning or an error, depending on how the attribute is configured

[System.Obsolete("use class ANew")]

class AOld

{

  public void Method() { }

}

class ANew

 {

    [System.Obsolete("use NewMethod", true)]

    public void OldMethod() { }

    public void NewMethod() { }

 }

static void Main(string[] args)

 { 

   // Generates 2 warnings:

   AOld aOld = new AOld();///Warn: is obsolete: use class ANew

   // Generate no errors or warnings:

   ANew aNew = new ANew();

   aNew.NewMethod();

   // Generates an error, terminating compilation:

   //aNew.OldMethod();//Error: is obsolete: use NewMethod

}

http://msdn.microsoft.com/en-us/library/22kk2b44%28v=vs.90%29.aspx 

http://msdn.microsoft.com/en-us/library/aa664623%28v=vs.71%29.aspx