What is a cookie, some time ago a cookie was only a small biscuit that went very well with a cup of tea or coffee, but since the advent of the world wide web a cookie is a small file that is stored on your computer created by a website that you have visited. The cookie contains information which is generally used to improve your experience of using a website.
For example, if your user ID and password are stored in a cookie, it saves you from typing in the same information all over again when accessing that website the next time. By keeping user history, cookies allow the Web site to tailor the pages and create a custom experience for that individual. Some web pages contain some script which reads the data in the cookie and so is able to carry information from one visit to the website (or related site) to the next.
Cookies can be divided into two types depending on their life span, i.e. how long the cookie is stored on your computer. The first type are short lived cookies which only exist as long as you have a session open on a webpage, the second are persistent cookies which expire after a specified time anything from a few hours to years.
A cookie in itself is not a problem, it is only a text file that can be used by the website that created it.
The problem with cookies is that they can be used by malevolent websites and programs to harvest information about you. Keeping a good security system up to date on your computer will ensure that your cookies are regularly checked.
As they say an ounce on the lips is equal to an inch on the hips, cookies can provide a pleasant experience but they can also have a down side. It is possible to check what cookies are stored on your computer using the tools in your browser. It is also possible to delete all cookies, but then be prepared to enter in your passwords when you login into your email and other accounts.