Computer system and file access control method capable of reducing danger that an unauthorized file, such as a malware, is accessed or executed

The object of the present invention is to reduce dangers of an unauthorized file, such as a malware, from being accessed (executed). The solution of the present invention is to provide a computer system which has a safe environment that is connected to a safe network and is not connected to a dangerous network, and a dangerous environment that is connected to the dangerous network and is not connected to the safe network. The computer system accepts file access from one of the environments, and determines whether the issuing source of the file is the safe environment or the dangerous environment. If the issuing source comes from the safe environment, the computer system adds the access path and the access type of the file access which originates from the safe environment into a white list which is a list of file information associated with an access permit.