An identification, user detection or, simply, web-tracking, all that means a computation and an installation of a special identificator for each browser visiting a certain site. By and large, initially, it was not designed as a ‘ global evil’ and, as everything else has another ‘ side of a coin’, in other words it was made up to provide a benefit, for example, to allow website owners to distinguish real users from bots, or to give them a possibility to save user’s preferences and use them during the further visits. However, at the same time this option catch promo’s fancy. As you know, cookies are the most popular way to detect users. And they have been being used in advertising since 90s.