A method of powering up a portable terminal, which automatically executes a software program when powered on, the terminal having a manually operated power-up key, wherein the method comprises the step of: a) at the beginning, moving (in 32) the key from an idle position in which the terminal is powered off to an active position in which the terminal is powered up, then b) before a first predetermined time interval (Δ1) has elapsed since the beginning of step a), starting (in 36) to run the software program on the terminal, the first time interval being long enough to check that the key has not been inadvertently moved, then c) when the first time interval elapsed, if the key is still in the active position, continuing (in 42) to run the software program, else powering down the terminal (in 40).