1. A method of manipulating the original content of at least one original read-only computer file in a computer file-system in a computer system, wherein the computer system comprises an operating system comprising a framework for in-line monitoring of accesses to the file-system, the method comprising: 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 file into a first file (F_ 1 ) and a second file (F_ 2 ); and associating the first file (F_ 1 ) with the second file (F_ 2 ) in the file-system.