Abstract: Secure data processing is carried out on a computer system with a higher-level or coordinated secure operating system that is not visible for a user. The secure operating system as a computer program application provides a virtual machine with virtual computer hardware on which a user operating system visible and usable for the user can be executed and which has at least one virtual mass memory with a file system of the user operating system or the secure operating system is encapsulated in a first virtual machine and the user operating system visible and usable for the user and equipped with at least one virtual mass memory with a file system is executed in a second virtual machine. The secure operating system cannot by manipulated by the user or a computer program application, in particular a harmful file.