Cookie is a mechanism by which a Web site provider temporarily writes data to a visitor's computer through a Web browser and saves it. In the cookie, data designated by the Web site (Web server) side can be saved, information on the user's identification and attributes, and the date and time of the last visit to the site are often recorded. When the user's ID and so on are saved in the site such as the net service, the user is automatically identified when the next access, and the service can be received as in the previous continuation. 4096 bytes of data can be recorded in one cookie and the number of cookies that one server can issue to the same computer is limited to 20 cookies. The total number of cookies is 300 pieces, and beyond this, it is deleted from the older one. In addition, each cookie has an expiration date set, and those past the deadline are discarded.