Cookies are simple uncompiled text files that help coordinate the remote website servers and your browser to display the full range of features offered by most contemporary websites. These features include hassle-free automatic logins and authentication, shopping cart functionalities, third party ad serving, ad management, preference setting, language setting, among many others. As cookie technology evolves along with website publishing and advertisement technology, privacy issues are sure to arise time and again.
Cookie-based ad tracking has evolved through the years. From simple operations like counting ad impressions, limiting popups, and preserving ad sequence, third party ad serving cookies have evolved to user profiling/website preference tracking. This latter group of activities—ad tracking, that has attracted a lot of controversy among online consumer privacy groups and other concerned parties. Many of the largest websites online use large-scale third-party ad serving networks which cover many sites. One of the largest is Google's Adsense/Adwords ad serving network. Literally, millions of pages run Adsense ads. For every click a valid user makes on a Google-served ad on their site, site owners make money ranging from pennies to dollars.