1. A computer program product for controlling a computer to generate mobile computing device malware definition data for use by a mobile computing device malware scanner executable upon a mobile computing device, said computer program product comprising: obtaining code operable to obtain from a data source master malware definition data, said master malware definition identifying a plurality of items of malware each belonging to one of a plurality of classes of malware threat; identifying code operable to identify one or more classes of malware threat against which said mobile computing device is to be protected; and generating code operable to generate from said master malware definition data said mobile computing device malware definition data, said mobile computing device malware definition data identifying items of malware identified within said master malware definition data which are within classes of malware threat against which said mobile computing device is to be protected.