  The one-loop structure of the trace anomaly is investigated using different
regularizations and renormalization schemes: dimensional, proper time and
Pauli-Villars. The universality of this anomaly is analyzed from a very general
perspective. The Euler and Weyl terms of the anomalous trace of the stress
tensor are absolutely universal. The pure derivative $ \square R$-term is shown
to be universal only if the regularization breaks conformal symmetry softly. If
the breaking of conformal symmetry by the regularization method is hard the
coefficient of this term might become arbitrary which points out the presence
of an ambiguous $ \int\sqrt{-g} R^2$-term in the effective quantum action.
These ambiguities arise in some prescriptions of dimensional and Pauli-Villars
regularizations. We discuss the implications of these results for
anomaly-induced inflationary scenarios and AdS/CFT correspondence.
