1. A method of determining a counterfeit security document, the security document having disposed thereon or therein coded data including a number of coded data portions, each coded data portion being indicative of: an identity of the security document; and, at least part of a signature, the signature being a digital signature of at least part of the identity; wherein the method includes: in a sensing device: sensing at least one coded data portion; and, generating, using the sensed coded data portion, indicating data indicative of: the identity; and, at least one signature part; in a processor: determining, from the indicating data: a determined identity; and, at least one determined signature part; determining if the security document is a counterfeit document using the determined identity and the at least one determined signature part.