| 摘要 |
A method of marking information to be produced in order to expose unauthorized copying. In the method, a user identifier (12a) is defined, a source file (10) containing a substantial part of the information produced is created, and a different target file (17) is created for each user on the basis of the source file (10) and the user identifier (12a). In the invention, several predefined modification rules (10b1-10b3, 31, 32) are stored in a file (10, 10b, 16) in order to modify the information contained in the source file (10). Using a digital processor, a sequence of modification keys (15a, 15b,...) is generated on the basis of the user identifier, the locations of the source file (10) to be modified are defined, and modifications are made in these locations, determining the nature and/or position of the modifications on the basis of the predefined modification rules (10b1-10b3, 31, 32) and modification keys (15a, 15b,...). From the content of the target file delivered to the user, it is possible to conclude a user-specific identifier and thereby the person responsible for the unauthorized copy.
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