A distributed system is disclosed in which one or more servers respond to requests for content including hyperlinks. Hyperlinks provide an interactive visual manifestation of an underlying reference to a resource. By using a graphical user interface provided by the device, a user is able to select a hyperlink, and thereby control the device to obtain the resource to which the underlying reference refers. However, if a user selects a hyperlink and the device is unable to follow the underlying reference to obtain the resource, user disappointment results. By arranging the server, on providing visual content including one or more hyperlinks, to attempt (212) to follow the references underlying the hyperlinks, and to alter (216) the appearance of any hyperlink for which the underlying reference could not be followed, users are alerted to the likelihood that selecting the hyperlink will not lead to them obtaining the resource. In this way, user disappointment is avoided. The technique is of particular utility to web-site administrators.