Abstract: Protection of a computer system (104) against attacks using malformed files is applied to an application (106) configured to process files of a predefined Headerless format indicated by a Characteristic pattern of bytes. An incoming file's Characteristic pattern is checked by comparing its leading bytes with Characteristic patterns. If its leading bytes have such a pattern, the file (100) is subjected to a full content check; the file is discarded (100) if it lacks such a pattern or has contents considered damaging. A file is checked regarding suitability for further processing by comparing its leading bytes with the Characteristic pattern of the predefined Headerless format. A full content check of the file may also be carried out. The application (106) is permitted to process files having the Characteristic pattern of the predefined Headerless format and appropriate file contents. The method can deal with ZIP files (b) etc.

Abstract: Protection of a computer system (104) against attacks using malformed files is applied to an application (106) configured to process files of a predefined Headerless format indicated by a Characteristic pattern of bytes. An incoming file's Characteristic pattern is checked by comparing its leading bytes with Characteristic patterns. If its leading bytes have such a pattern, the file (100) is subjected to a full content check; the file is discarded (100) if it lacks such a pattern or has contents considered damaging. A file is checked regarding suitability for further processing by comparing its leading bytes with the Characteristic pattern of the predefined Headerless format. A full content check of the file may also be carried out. The application (106) is permitted to process files having the Characteristic pattern of the predefined Headerless format and appropriate file contents. The method can deal with ZIP files (b) etc.