The present invention relates to a method and system of controlling the writing of data to a computer storage medium such as a hard drive in a computer system in order to prevent viruses or similar program code from being saved on such medium. Upon the computer system initiating a request to write data to the medium, the application embodying the method and system checks the identity of the running application requesting to perform the write. The method and system then checks a rule database to determine if such requesting application has permission to write to the medium. The system can also check that the data file type that the application seeks to write is a permitted type for that application. In response to the output of the database check, the requested write is allowed to proceed or is blocked. In the absence of a rule, the system presents the request to the computer user. The user can either grant permission or block, and such response can be included in the rule database. User responses can be collected from many instances of the invention and the collective response of users presented to a user.