Method of protecting a computing system from harmful active content in documents

A method for protecting a computing device from potentially harmful code in a document, the method comprising:

• receiving a data structure representation of the document;
• providing one or more definitions of potentially harmful active content in 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;
• dynamically editing by a user the editable configuration file by adding a new definition
• parsing the editable configuration file to generate a data structure representation of the definitions in the editable configuration file;
• comparing the data structure representation of the document with the data structure representation of the definitions of potentially harmful active content to identify potentially harmful active content within the document;
• and
• modifying the document to render harmless any identified potentially harmful active content before presenting the document to the computing device.