[en] The theoretical information threshold for the planted clique problem is , but no polynomial algorithm is known to recover a planted clique of size , . In this paper we will apply a standard method for the analysis of disordered models, the parallel tempering (PT) algorithm, to the clique problem, showing numerically that its time-scaling in the hard region is indeed polynomial for the analyzed sizes. We also apply PT to a different but connected model, the sparse planted independent set problem. In this situation thresholds should be sharper and finite size corrections should be less important. Also in this case PT shows a polynomial scaling in the hard region for the recovery. (paper: interdisciplinary statistical mechanics)