'Normal' cookies are a type of data saved by a website onto the user's computer during a visit to the site. Cookies are not malware and are not inherently malicious - they do not harm the computer system or the user's stored information. Due to privacy concerns however, they are often unwanted.
'Tracking' cookies are a specialized type of cookie that can be shared by more than one website. Though tracking cookies may be used by websites to present a visitor with customized content, they can also potentially be used to track a user's web browsing behavior. As such, they may pose a slight risk to a user's privacy.
Almost all modern web browsers now offer users the ability to disable cookies, ensuring their web browsing history is not recorded. Unfortunately, many websites require cookies to function correctly, so the user must carefully evaluate the costs and benefits of cookie use and how their privacy and web browsing experience may be affected.
How Cookies Work
Normally, when a user visits a website, the site saves a small text file, known as a cookie, onto the user's system. This file identifies the user as a unique visitor to that site and contains a 'record' of the actions performed or preferences set during the visit, for example, the last page viewed or the saved contents of the user's online 'shopping cart'. If the user later returns, the site can then 'read' the saved cookie and display the appropriate content.
Unlike a normal cookie, a tracking cookie can be used by more than one site. Because a single tracking cookie may contain a history of the user's actions on multiple sites, if these cookies are misused or exploited the saved information may be used to analyze the user's web browsing behavior.
Tracking Cookies and Advertising
For example, when a user visits a site that hosts third-party banners, the advertising service may save a cookie on the user's system indicating what banners have already been displayed. If the user subsequently visits another site that uses the same advertising service, the second site can 'read' the same cookie and be directed to display a new set of banners - while the service logs that the user has visited both sites.
Advertising services typically collate data from thousands or even millions of users in order to analyze site statistics and general web trends, ultimately to facilitate targeted advertising. As this type of data mining involves vast amounts of data, it is highly unlikely that any individual's habits are closely examined. Many users however still express discomfort at the idea of their web browsing habits being tracked.
Most modern web browser provide users with the option of disabling cookies, preventing them from being saved on the computer. Alternatively, many privacy-conscious users clear their browser cache after every web browsing session in order to delete the saved cookies. Many antispyware and comprehensive antivirus solutions also block tracking cookies.
Do note that many websites do not function correctly if cookie use is not enabled. For example, many websites with password-protected areas and retail sites with shopping cart systems usually require cookies to be enabled in order to work.
Examples of Tracking Cookies include: