There is a great deal of effort directed towards attacking smart cards and tokens to reveal secret information and a similar degree of effort for the design and provision of effective countermeasures. Some of the most interesting attacks (e.g. DPA) make use of side channel leakage and so the corresponding countermeasures attempt to make it impractical to extract useful content from the leaked signals. However there are always occasions when the desired secret information is obtained either by very advanced and expensive attacks or by human engineering. The problem is then how to detect the cloned devices. It is no longer difficult to find a platform that can host a duplicated application; however it is very unlikely to be the same platform as the original. The suggestion is to consider the card leakage as representing a "fingerprint" for the card platform that is difficult to duplicate in a cloned device.