Abstract: A method and system are disclosed for securely distributing a plurality of software files from a software distribution processor to a user processor, while selectively enabling the user processor to only use a subset of a lesser plurality of the software files. This is achieved by employing a customer key which includes a clear customer number and a derived portion derived from the customer number. The customer key is transformed into a second customer key which serves as a key expression for encrypting a file encryption key specifically intended for a respective one of the plurality of files. A plurality of software files can be stored together, for example on a CD-ROM, with each file encrypted under a corresponding file encryption key. The CD-ROM can be distributed to many user processors. When a specific user processor needs to run one of the software files, a request will be transmitted from the user processor to the software distribution processor.