Cookies enable web sites to monitor their users’ web surfing habits and profile them for marketing purposes (for example, to find out which products or services they are interested in and send them targeted advertisements).
Cookies come in different flavours:
Cookies that are stored in the computer’s memory only during a user’s browsing session and are automatically deleted from the user’s computer when the browser is closed.
These cookies usually store a session ID that is not personally identifiable to users, allowing the user to move from page to page without having to log-in repeatedly. They are widely used by commercial web sites (for example, to keep track of items that a consumer has added to a shopping cart).
Cookies that are stored on the user’s computer and are not deleted when the browser is closed. Permanent cookies can retain user preferences for a particular web site, allowing those preferences to be used in future browsing sessions.
Permanent cookies can be used to identify individual users, so they may be used by web sites to analyse users’ surfing behaviour within the web site. These cookies can also be used to provide information about numbers of visitors, the average time spent on a particular page and generally the performance of the web site. They are usually configured to keep track of users for a prolonged period of time, in some cases many years into the future.
If you have Adobe Flash installed on your computer (most computers do), small files may be stored on your computer by websites that contain Flash media, such as video clips. These files are known as Local Shared Objects (LSOs) or Flash cookies. They can be used for the same purposes as regular cookies (properly called HTTP cookies).
Flash cookies can also back up the data that is stored in a regular cookie. When you delete cookies using your browser controls, your Flash cookies are not affected. So a website that served a cookie to you may recognise you on your next visit if it backed up its now-deleted cookie data to a Flash cookie.
A server cannot set a cookie for a domain that it is not a member of. In spite of this, users quite often find in their computer files cookies from web sites that they have never visited. These cookies are usually set by companies that sell internet advertising on behalf of other web sites. Therefore it may be possible that users’ information is passed to third party web sites without the users’ knowledge or consent, such as information on surfing habits. This is the most common reason for people rejecting or fearing cookies.