Abstract. Given a non-semisimple automorphism ϕ of a vertex algebra V , the fields in a ϕ-twisted V -module involve the logarithm of the formal variable, and the action of the Virasoro operator L0 on such module is not semisimple. We construct examples of such modules and realize them explicitly as Fock spaces when V is generated by free fields. Specifically, we consider the cases of symplectic fermions (odd superbosons), free fermions, and βγ-system (even superfermions). In each case, we determine the action of the Virasoro algebra.