A memory power control unit, MPCU, is provided for preventing unauthorised access to data stored in a volatile memory, the MPCU comprising a power controller comprising an input configured to receive a signal from a tamper detection circuit, a first supply input configured 5 to receive a first supply voltage, a first reference input configured to receive a first reference voltage, a supply output configured to output a supply voltage to the volatile memory, a reference output configured to output a reference voltage to the volatile memory, wherein, in response to receipt of a signal at the input indicative of an attempt to tamper with the volatile memory, the power controller is configured to output a reduced supply voltage via the supply 10 output for a first predetermined time period, wherein the reduced supply voltage is less than the first supply voltage.