A method of identifying fraudulent activity from a user device using a chain of device digital fingerprints, the method comprising: calculating a digital fingerprint of a device belonging to a user accessing an online service, wherein the calculated digital fingerprint is associated with one time instance indicating when the user accessed the online service: determining, from a multitude of all known fingerprints of devices, a group of digital fingerprints in which the calculated digital fingerprint of the device belonging to the user is present, wherein a measure of similarity between any given pair of fingerprints from different groups is equal to zero; calculating vectors of features for changed features of the digital fingerprint of the device belonging to the user and of each digital fingerprint within the determined group of digital fingerprints, an analysis module being configured for calculating a matrix of joint pairwise probabilities of changed features of each digital fingerprint and for identifying columns and rows respectively corresponding to a vector of changed features from the matrix of joint pairwise probabilities; using the calculated vectors of features, calculating a probability that the calculated digital fingerprint of the device belonging to the user and each digital fingerprint within the determined group belong to a same chain of digital fingerprints, wherein the chain of digital fingerprints comprises a chronologically ordered sequence of digital fingerprint values associated with the device; identifying digital fingerprints of a set of candidate devices from the digital fingerprints of the group whose probability of belonging to the same chain of digital fingerprints exceeds a threshold value; comparing the calculated digital fingerprint of the device with the digital fingerprints of devices in the set of candidates; determining that the device corresponds to one of the devices identified in the set of candidates when the comparison results in a match higher than a specified threshold; in response to determining that the device corresponds to one of the devices in the set of candidates, permitting user interactions with the online service, and in response to determining that the device does not correspond to one of the devices in the set of candidates, tracking the user interactions with the online service as fraudulent activity. calculating a digital fingerprint of a device belonging to a user accessing an online service, wherein the calculated digital fingerprint is associated with one time instance indicating when the user accessed the online service: determining, from a multitude of all known fingerprints of devices, a group of digital fingerprints in which the calculated digital fingerprint of the device belonging to the user is present, wherein a measure of similarity between any given pair of fingerprints from different groups is equal to zero; calculating vectors of features for changed features of the digital fingerprint of the device belonging to the user and of each digital fingerprint within the determined group of digital fingerprints, an analysis module being configured for calculating a matrix of joint pairwise probabilities of changed features of each digital fingerprint and for identifying columns and rows respectively corresponding to a vector of changed features from the matrix of joint pairwise probabilities; using the calculated vectors of features, calculating a probability that the calculated digital fingerprint of the device belonging to the user and each digital fingerprint within the determined group belong to a same chain of digital fingerprints, wherein the chain of digital fingerprints comprises a chronologically ordered sequence of digital fingerprint values associated with the device; identifying digital fingerprints of a set of candidate devices from the digital fingerprints of the group whose probability of belonging to the same chain of digital fingerprints exceeds a threshold value; comparing the calculated digital fingerprint of the device with the digital fingerprints of devices in the set of candidates; determining that the device corresponds to one of the devices identified in the set of candidates when the comparison results in a match higher than a specified threshold; in response to determining that the device corresponds to one of the devices in the set of candidates, permitting user interactions with the online service, and