System.Security.Cryptography.RSA.DerivedClassMustOverride C# (CSharp) Method

        private static Exception DerivedClassMustOverride()
        {
            return new NotImplementedException(SR.NotSupported_SubclassOverride);
        }

 protected virtual byte[] HashData(Stream data, HashAlgorithmName hashAlgorithm)
 {
     throw RSA.DerivedClassMustOverride();
 }