Need help in Sending E-mail Via .Net

Question

Hello Friends,
                       When I tried to send an E-mail through .Net using the following code,
           MailMessage msg = new MailMessage("[email protected]","[email protected]","VS2008 Mail","VS2008 Mail Check");
         
               SmtpClient client = new SmtpClient("smtp.mail.yahoo.com");

             client.Send(msg);

          I got a message as below:

             "The Smtp Server requires a secure connection or the client was not Authenticated...."

              Then it Exits! Can any one of you help me in sorting out this problem.

                                                      Thank You in Advance!
                                                                                                                                                                         Sincerely,
                                                                                                                                                                         V.Hilbert