During backup of a database's data stored in individual files, it is not permissible for the data in the individual files to be altered, for reasons of consistency. For this reason, the files are blocked to altering access operations after a particular time during a backup operation. According to the invention, the backup operation is carried out in two parts. First, the files are transferred without there being any alteration block. A recording file is used to note files which are altered during transferring. These files are transferred again in a second part. During the second part an alteration block is required. It can be assumed that the number of files needing to be transferred in the second part is much smaller than the number of files needing to be transferred in the first part. For this reason, a significantly shortened alteration block is achieved.