Cookies are managed by a browser and contain information that allows tracking sites to build profiles of the websites visited by a user.

Each time a user visits a new website, the tracking site can review those cookies to offer ads that might be relevant to the user.Wills says social networks go to far by allowing the transmission of unique identifiers. Users put a lot of information about themselves on social networking sites, said Wills.A lot of that information can be seen by other users, by default.