A software program is configured in accordance with a software aging process such that one or more files generated by the program are at least partially encrypted using a cryptographic key associated with a current time interval for which the files are generated. The cryptographic key may be a symmetric key used for both encryption and decryption operations, such that cryptographic key used for encryption in a given interval is also required to decrypt files encrypted during that interval. Periodic updates of the software program are provided to a legitimate user of the software program, with a given one of the updates including a different cryptographic key associated with a subsequent time interval. The cryptographic key associated with a particular one of the time intervals may be common to each of a set of legitimate copies of the software program that have received the corresponding version of the periodic update. The variation of the cryptographic keys from one interval to another discourages unauthorized use of the software program by deliberately requiring both legitimate and illegitimate users to request unusually frequent updates, thereby substantially increasing the tracing and prosecution risks borne by software pirates.