They cannot be used to gather sensitive information such as the fields in a Netscape preference file. Cookies are passive files that are delivered to the client, stored on the client's hard drive, and returned in certain situations to the same server that provided the information in the first place. The filename is different for each platform. Client state information can be stored in several ways. For example, server administrators and programmers can create a database application that tracks and stores data they would otherwise have managed with cookies.
Cookies are simply a programming convenience.
A Web site may set an expiration date for a cookie it delivers. If no expiration date is specified, the cookie is deleted when the user quits Netscape Navigator. Cookies are designed to be read only by the site that provides them, not by other sites. While the cookie file itself is unencrypted on the user's computer, it can be encrypted between the user's computer and a Web site. The SSL session handles the actual encryption of cookie data.