Wikipedida Wikimedia query returns 403 forbidden

I had the following webclient request 
 WebClient serviceRequest = new WebClient();
var JsonResponse = serviceRequest.DownloadString(new Uri(urselected));

Where urselected was the REST query string. The query worked fine in my browser but returned 403 forbidden error. I found the following post which addresses the problem:

Wikipedia query returns error 403

Modified my code as follows and it worked find:

WebClient serviceRequest = new WebClient();
           serviceRequest.Headers.Add("user-agent", "Silver Azure");

           var JsonResponse = serviceRequest.DownloadString(new Uri(urselected));