A method and system are provided for authenticating a communication device. The method conducted at a remote server includes the steps of: receiving, from a communication device via a first communication channel, a fingerprint identifying the communication device and a value of a parameter of the communication device specific to the communication device and variable over time; determining whether the value is within a predicted range; and if the value is not within the predicted range or the predicted range has not been established, sending an additional authentication request via a second communication channel. The predicted range is learnt over a given number of interactions between the communication device and the remote server and an expected rate of change of the value.