A virtual machine includes a shadow memory, a shadow disk, and a virtual NIC. A virtual machine includes a guest OS. The shadow memory and the shadow disk each store therein pieces of data and pieces of tag information assigned to the pieces of data, so as to be kept in correspondence with one another. When malware transmits data, the virtual NIC generates the transmission information containing the transmitted data and tag information assigned to the transmitted data and further transmits the generated transmission information to the virtual machine. The guest OS extracts the tag information from the received transmission information. Further, the guest OS determines a transfer destination of the transmission information on the basis of the extracted tag information and further transfers the transmission information to the determined transfer destination.