This is useful for having the browser remember some specific information. Temporary cookies are most often used to associate a specific user's browser with information about that session stored on a server. The data stored in a temporary cookie is usually a globally unique id number. These cookies are routinely destroyed when your browser is closed.
Persistent cookies are more permanent.
An HTTP Cookie cannot be used to get data from your hard drive, get your email address or steal sensitive information about your person. Early implementations of Java and JavaScript could allow people to do this but for the most part these security leaks have been plugged. We use both types of cookies on this site. You may elect to have NOT have the system remember you, in which case we will not write out a permanent cookie on your system. You will then need to provide us with this information on subsequent visits to the site.