One of the main concerns in a tokamak is the risk of disruptions with asymmetric halo currents flowing partially in the plasma and partially in the surrounding structures. A detailed 3D description of the full torus is therefore needed. This paper proposes a method for the 3D halo current analysis based on an integral formulation, exploiting compression techniques, parallel architectures, and suitable preconditioners. The procedure is shown to work in an ITER-like geometry.