Epitaxial YBa2Cu3O7 thin films, grown by high-pressure dc sputtering, are irradiated with He+ ions at 80 keV with doses between 1014 and 1015 cm-2. Irradiation reduces the critical temperature but it does not modify the carrier concentration. Angle-dependent resistivity is used to show that the mass anisotropy does not change upon irradiation. The melting transition in magnetic fields applied parallel to the c axis is analyzed by I-V critical scaling, and all irradiated and nonirradiated samples show a three-dimensional vortex glass transition with the same critical exponents. The dissipation in the liquid state is analyzed in terms of the activation energy of the magnetoresistance in a perpendicular magnetic field. While as-grown samples show an activation energy depending as 1/H on the applied magnetic field, irradiated samples show a dependence as 1/H0.5, characteristic of plastic deformation of vortices. This is discussed in terms of the point disorder introduced by ion irradiation.