Hyperlinks in the Attribute Viewer in Silverlight are unusable.
Additional configuration is necessary for the Silverlight viewer to interpret this data as a hyperlink.
- Using ArcMap, open the .mxd that the mapservice is published from.
- Open the Properties for the layer which contains hyperlinks.
- If necessary, select the Display tab.
- Verify that the box for Hyperlinks is enabled and that the correct field is selected.
- Also verify that the type is 'URL'.
- Save and close the .mxd.
- Republish the mapservice if necessary (ArcGIS Server 10.1 or later)