Embodiments of the invention relate to manipulating the original content of at least one original read-only computer file in a file-system of a computer system, where the computer system includes an operating system including a framework for in-line monitoring of accesses to the file-system. An exemplary embodiment, includes transforming the original content via a non-length-preserving data transformation algorithm, thereby resulting in transformed content, storing the transformed content in a transformed computer file, splitting the transformed computer tile into a first file and a second file, and associating the first file with the second file in the file-system. The non-length-preserving data transformation algorithm includes a length-increasing data transformation algorithm.