Method and system protecting against identity theft or replication abuse

A method, implemented by a computer-implemented authentication system, for authenticating a user attempting to access a target component of a computer system, the method comprising:

• a) receiving, from a first user system via a computer network, user authentication information and a network address identifying the first user system within the computer network;
• b) obtaining at least one data item of contextual information indicative of a property of an environment of a wireless communications device associated with the user authentication information;
• c) authenticating the user based on at least the user authentication information;
• and
• d) subject to successful authentication, granting access to the target component and maintaining a data record indicative of a security context comprising the received network address and the received contextual information;
• wherein the method further comprises:
• determining, based on one or more selection criteria, at least one recurrent security context from a plurality of stored data records, the recurrent security context having occurred a number of times, each data record being indicative of a stored security context comprising one or more network addresses of a user system and received contextual information associated with said one or more network addresses, and each stored security context having associated with it data about one or more previous occurrences of said stored security context;
• and
• using the determined recurrent security context in a subsequent decision whether to grant a subsequent request by said user to access the target component.