  Finite temperature lattice QCD is probed by varying the temporal boundary
conditions of the fermions. We develop the emerging physical behavior in a
study of the quenched case and subsequently present first results for a fully
dynamical calculation comparing ensembles below and above the phase transition.
We show that for low temperature spectral quantities of the Dirac operator are
insensitive to boundary conditions, while in the deconfined phase a non-trivial
response to a variation of the boundary conditions sets in.
