Add warning for Cyberduck and Duo.

content/handling_data/data_transfer/cyberduck.md

@@ -9,6 +9,12 @@ weight = "30"
 ## Using Cyberduck
 ---------------
 
+{{% notice warning %}}
+Recent versions of Cyberduck are known to be incompatible with Duo. Until the issue is
+fixed, **HCC recommends using version 8.4.3**, which can be downloaded [here](https://cyberduck.io/changelog/).
+{{% /notice %}}
+
+
 If you wish to use a GUI for data transfer, be aware that not all programs will function
 correctly with Duo two-factor authentication.  Mac users are recommended
 to use [Cyberduck](https://cyberduck.io). It is compatible with Duo, but a