A method of determining that a subject electronic device 1021 . . . N is counterfeit. The method involves delivering the web page component to a subject 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 device 1021 . . . N. Reference values of the plurality of attributes are retrieved from a device property store 110 and the method determined that the subject 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.