Traditionally, auditors followed a paper ‘audit trail’ from source documents to final accounts and vice versa. With the advent of computerised business systems, auditors modified their approach to ‘audit around the computer’ by comparing source documents before processing with output reports after processing, and treating the computer as a mysterious ‘black box’ in the middle. In the twenty-first century this approach is no longer possible. In many cases there are no source documents, and data and files are only available in machine-readable form and not on paper documents.