Method and apparatus for communicating data between computer devices

A client server system (100, 200, 300) comprises a client subsystem (100), a server subsystem (200) and an interconnecting data network. The client subsystem includes a client application (110, 120, 130, 140, 150) operable to initiate a secure connection over the interconnecting network with the server subsystem (200). The server subsystem includes a server application (254, 255, 256, 257), whichis operable to co-operate with the client application to complete the setting up of a secure connection with the client application upon initiation of the connection by the client application and which is further operable to transmit output data over such a connection in response to requests for service provided by the client application. The server subsystem further includes a notification server (220) and the server application is additionally operable to generate a notification, in response to detecting the occurrence of an event in the absence of a secure connection between the server application and the client ap