1. A data processing system ( 102 ) comprising a runtime environment ( 110 ) with scripting engine means for executing a script, wherein: the scripting engine means implements a public scripting engine ( 112 ) and a private scripting engine ( 114 ); the runtime environment is configured to have the script executed by the public scripting engine if the script does not require access to a pre-determined resource ( 124 ; 126 ) at the system; the runtime environment is configured to have the script executed by the private scripting engine if the script requires access to the pre-determined resource; only the private scripting engine has an interface ( 120 ; 130 ) for enabling the script to access the predetermined resource; and the scripting engine means is configured to prevent the private scripting engine from communicating data to the public scripting engine or to a server ( 106 ) external to the data processing system, unless such communication has been approved.