1. A method for estimating a number of accessing entities which are accessing a website, the method comprising: dividing a period of time for which the number of accessing entities is to be estimated into a plurality of time intervals; providing a plurality of arrays of bits, the number of the arrays of bits corresponding to the number of time intervals and each array of bits having a number of S bits; associating each array of bits with one of the plurality of time intervals, respectively; repeatedly determining that the website is accessed by an accessing entity during each of the plurality of time intervals; determining, in reaction to each access of the website by an accessing entity during a current time interval of the plurality of time intervals, identification data comprising a characterizing number x dependent on the accessing entity, each accessing entity being characterized by a characterizing number x taken from the interval 0 to M−1; calculating, in reaction to each access of the website by an accessing entity during a current time interval of the plurality of time intervals, a hash bucket H(x) for the accessing entity by mapping the characterizing number x dependent on the accessing entity onto a value between 0 and S−1 according to a non-linear mapping function H(x); activating, in reaction to each access of the website by an accessing entity during a current time interval of the plurality of time intervals, the bit corresponding to the determined hash bucket H(x) for the accessing entity in the array of bits corresponding to the current time interval; determining, after the end of the period of time, a combined array of bits by combining the plurality of arrays of bits associated with the plurality of time intervals by using a logical OR-operation between the bits of the arrays of bits having the same significance; and estimating the number of accessing entities of the website which accessed the website during the period of time based on the activated bits of the combined array of bits.