Abstract: The invention provides a security system for preventing unauthorised dispensing of cash from a cash dispenser (5), the cash dispenser (5) being located inside a physically protected area (10) of a cash handling machine (1), the cash handling machine having a host controller (2) outside the physically protected area (10) configured to issue dispensing instructions to the cash dispenser (5) over a dispensing instruction data link (3), the security system comprising: an access permission device (11) located inside the physically protected area (10) configured and connected to receive verification signals over a verification data link (2, 3, 22) and to block transmission of dispensing instructions over the dispensing instruction data link (3) to the cash dispenser if the verification signals are not received or are received but are incorrect; and access permission software operatively associated with the host controller (2) configured to send the verification signals to the access permission device (11).