1. A computer program product for protecting a computing device from potentially harmful code in a document, the computer program product comprising: a non-transitory computer readable storage medium having computer readable program code embodied therewith, the computer readable program code comprising: computer readable program code configured to receive a data structure representation of the document; computer readable program code configured to add dynamically one or more definitions of potentially harmful active content to an editable configuration file, each definition identifying potentially harmful active content and specifying an action to be performed on that potentially harmful active content if that potentially harmful active content is found in the document; computer readable program code configured to parse the editable configuration file to generate a data structure representation of the one or more definitions in the editable configuration file; computer readable program code configured to compare the data structure representation of the document with the data structure representation of the one or more definitions of potentially harmful active content to identify potentially harmful active content within the document; and computer readable program code configured to modify the document to render harmless any identified potentially harmful active content before presenting the document to the computing device.