Virtual tensile experiments on cylindrical copper wires of nanometric diameter were carried out using molecular dynamics techniques based on the embedded-atom method. Transverse, atomically sharp surface cracks with circular fronts of different depths are introduced to evaluate their effect on the mechanical strength of the nanowires. The axisymmetric z-axis of the specimen is on the 001 direction of the nanowires. The analysis shows that, at 0 K, the cracked Cu nanowires behave in a ductile manner, their strength being determined by dislocation or twinning nucleation from the crack tip. Their calculated fracture toughness ranges from 0.6 to 3 MPa√m.