Abstract: Methods and apparatus are provided for causing the incorrect operation (‘faults’) of digital devices such as embedded computer systems or integrated circuits. The apparatus uses a switching element to cause perturbations on the power supplies of the digital device. This apparatus can be connected to existing embedded systems with a minimal of modifications, and can insert a variety of faults into those embedded systems. Such faults can be used for verification of fault-tolerant systems or algorithms, including both safety-critical designs and cryptographic designs.