  We study the critical properties of three dimensional frustrated magnets,
diluted with non-magnetic impurities. We show that these systems exhibit a
second order phase transition, corresponding to a new universality class. In
the pure case, the phase transition is expected to be weakly of first order. We
therefore argue that these frustrated systems can be used to study
experimentally the rounding effect of disorder on discontinuous phase
transitions. We give first estimates of the critical exponents associated with
this universality class, by using the method of the effective average action.
