Build 4.0.0.38 of xlsgen makes sure that encrypted XLS and XLSX files (and their variants) are re-encrypted automatically when the file is written back after an update. The re-encryption uses the same algorithms and parameters than the decryption, which means xlsgen is neutral. This comes as an expectation since there is no ground for xlsgen removing the protection in a file without the client program asking for it (by resetting the password).