A method of preventing a subject communication device 1021 . . . N from accessing a resource when it is determined to be counterfeit. The method involves delivering the web page component to a subject communication device 1021 . . . N in response to a request. The web page component is adapted to retrieve actual values of a plurality of attributes from the subject communication device 1021 . . . N. Reference values of the plurality of attributes are retrieved from a device property store 110 and the method determines that the subject communication device 1021 . . . N is counterfeit when at least one of the actual values of the plurality of attributes is different to the reference value of that attribute.