A method, system, and computer program product for managing user identification codes in an interne advertising environment. One aspect implements a system including a database engine to store a plurality of signals comprising characteristics and/or values received from a user device. A user ID generator calculates collision statistics and/or fragmentation statistics to form a first mapping function that is in turn used to generate a plurality of identification codes based at least in part a first set of selected signals. A calibration module produces measurements determined from collision quantities and/or fragmentation quantities using the first mapping function, wherein the measurements are determined by comparing the plurality of identification codes to entries in a known ID database. A sequencing module generates updated sequences of mapping functions.