A system for blocking an external attack, the system comprising: a network file server; and a network file server, NFS, client installed in a user terminal or a service server and communication-connected with the network file server which is remotely positioned, wherein the network file server is adapted to verify, when there is an access or opening request of a file stored in the network file server mounted in the user terminal or service server in a network drive format from the NFS client, program information of a program requesting the access or opening and is adapted to determine whether the access or opening request is authorized according to the verified program information and to block the access to the file which is requested to be accessed or provide the file of which opening is requested to the NFS client only in a read only mode when the access or opening request is unauthorized according to a determination result, characterised in that the NFS client is adapted to verify by which corresponding program the access or opening request is requested and to add program information of the corresponding program to the request and transfer the program information to the network file server, and the network file server is adapted to verify whether the corresponding program corresponds to a previously designated program based on the received program information and to block the access of the file which is requested to be accessed or provide the file of which opening is requested to the NFS client only in the read only mode when the corresponding program does not correspond to the previously designated program, when the opening request is an opening request of a file browsing program provided by the operating system installed in the user terminal or the service server, the network file server is adapted to provide the file of which the opening is requested to the NFS client in a read/write mode. a network file server; and a network file server, NFS, client installed in a user terminal or a service server and communication-connected with the network file server which is remotely positioned, wherein the network file server is adapted to verify, when there is an access or opening request of a file stored in the network file server mounted in the user terminal or service server in a network drive format from the NFS client, program information of a program requesting the access or opening and is adapted to determine whether the access or opening request is authorized according to the verified program information and to block the access to the file which is requested to be accessed or provide the file of which opening is requested to the NFS client only in a read only mode when the access or opening request is unauthorized according to a determination result, characterised in that the NFS client is adapted to verify by which corresponding program the access or opening request is requested and to add program information of the corresponding program to the request and transfer the program information to the network file server, and the network file server is adapted to verify whether the corresponding program corresponds to a previously designated program based on the received program information and to block the access of the file which is requested to be accessed or provide the file of which opening is requested to the NFS client only in the read only mode when the corresponding program does not correspond to the previously designated program, when the opening request is an opening request of a file browsing program provided by the operating system installed in the user terminal or the service server, the network file server is adapted to provide the file of which the opening is requested to the NFS client in a read/write mode.