Cookie

Cookies are tiny chunks of data that Web sites hand to and receive from your Web browser in an effort to capture aggregate Web-site statistics or store your login preferences.

The way cookies are created is simple: When your browser makes a request to a Web server the server replies and a special field in the response header instructs your browser to store the cookie data supplied by the server.

The cookie data is defined by six parameters. These are the cookie name, its value, the expiration date, the path for which the cookie is valid, the domain the cookie is valid for and whether a secure connection must be available when the browser returns cookie data to a server.

The designers of the cookie system never considered that someone might not want cookies to expire, so you'll often see cookies with expiration dates such as some date and time in 2038.

2038 is often the maximum year used for a really dumb reason: Active Server Pages in Microsoft Internet Information Server 3.0 and 4.0 and Microsoft Internet Information Services 5.0 have a small bug that causes an error - we quote from Microsoft Knowledge Base article Q247348: "This is caused by an overflow of the time_t variable in the C/C++ programming language. This variable is a 32-bit integer value used as an offset in seconds from January 1, 1970. This variable has a maximum value of 2147483647, which only allows dates through 3:14:07 GMT on January 19, 2038."

From Cookie cookery, Gearhead, Network World, 09/09/02.