A method for monitoring control-flow integrity in a low-level execution environment, the method comprising receiving, at a monitor, a message from the execution environment indicating that the execution environment has entered a controlled mode of operation, receiving, at the monitor, a data packet representing execution of a selected portion of a control-flow process at the execution environment, identifying, using the data packet, a pathway corresponding to the selected portion of the control-flow process from a set of permissible control-flow pathways and determining whether the identified pathway corresponds to an expected control-flow behaviour.