1. A method for securely managing user access to a file system, comprising: providing a secure device comprising a Universal Serial Bus (USB) flash drive, wherein the secure device is adapted to establish a connection to a server; establishing the connection between the secure device and the server using a secure sockets layer (SSL)/transport layer security (TLS) authentication; receiving, at the secure device and through the established connection, a plurality of data pertaining to a virtual tree file system, wherein the virtual tree file system comprises a plurality of files which are stored outside the secure device; processing the user request at the secure device according to an updated use permission associated to an internal file, wherein the updated use permission is obtained at the secure device by updating a use permission based on permission data sent from the server through a connection established between the secure device and the server; exposing, at the secure device, the virtual tree file system to a user based on the data received from the server, wherein the virtual tree file system is navigable by the user; receiving a request for accessing a file in the virtual tree file system; wherein the file is fetched externally to the secure device from the server via the server according to a server policy; displaying to the user with a display of the secured device, the file in the virtual tree file system through the established connection, the file being presented on the display and not cached locally in the memory in the secured device; and receiving, at the secure device and through the established connection, updated data pertaining to an updated virtual tree file system comprising a plurality of files which are at least partly stored outside the secure device and partly stored inside the secure device; and exposing, at the secure device, the updated virtual tree file system to the user based on the updated data received from the server; wherein the updated virtual tree file system is navigable by the user; and wherein a file stored on a memory of the secure device, which is identified in a previously exposed file system and not identified in the updated file system, is removed from the memory of the secure device.