Use default credentials for the proxy if none provided

The UseDefaultCredentials on WebClient (if true) will send creds to the server if requested not the proxy. The Proxy object on WebClient is a IWebProxy which only has a Credentials member (yes could probably cast to WebProxy). This change will send the default creds to the default proxy server

Files/dropper.cs

@@ -65,7 +65,8 @@ public class Program
 			proxy.BypassProxyOnLocal = false;
 			x.Proxy = proxy;
 		} else {
-			x.UseDefaultCredentials = true;
+			if (null != x.Proxy)
+				x.Proxy.Credentials = CredentialCache.DefaultCredentials;
 		}
 
 		var df = "#REPLACEDF#";