A method of validating machine components in a self-service terminal is disclosed which comprises providing at least one machine component with a machine readable identifier and reading identity data from the machine readable identifier using a processing unit. The identity data is compared with identity data stored in the memory of the processing unit to determine if the identity of a component has changed. If the identity has changed, the processing unit compares the identity data with source data to determine if the component is from a trusted source. In one embodiment, the self service terminal is an ATM and the components are an encrypting Personal Identification Number (PIN) pad, a cash dispenser unit and a card reader.