  Electric conductivity is sensitive to effective cross sections among the
particles of the partonic medium. We investigate the electric conductivity of a
hot plasma of quarks and gluons, solving the relativistic Boltzmann equation.
In order to extract this transport coefficient, we employ the Green-Kubo
formalism and, independently, a method motivated by the classical definition of
electric conductivity. To this end we evaluate the static electric diffusion
current upon the influence of an electric field. Both methods give identical
results. For the first time, we obtain numerically the Drude electric
conductivity formula for an ultrarelativistic gas of quarks and gluons
employing constant isotropic binary cross sections. Furthermore, we extract the
electric conductivity for a system of massless quarks and gluons including
screened binary and inelastic, radiative $2\leftrightarrow 3$ perturbative QCD
scattering. Comparing with recent lattice results, we find an agreement in the
temperature dependence of the conductivity.
