use the below namespace
localhost.MyWebService myService = new localhost.MyWebService();
System.Net.CredentialCache myCredentials = new System.Net.CredentialCache();
NetworkCredential netCred = new NetworkCredential("UserName", "Password");
myCredentials.Add(new Uri(myService.Url), "Basic", netCred);
myService.Credentials = myCredentials;
// Now call methods on the myService object...
we should be aware that by using Basic Authentication the user name and password are sent as Base 64 encoded text. That is as secure as sending it as plain text, so the best way to use this authentication mechanism is in combination with SSL. This way, the data is encrypted .