We study the robustness of Barabási-Albert scale-free networks with respect to intentional attacks to highly connected nodes. Using the simulated annealing optimization heuristic, we rewire the networks such that their robustness to network fragmentation is improved but without changing neither the degree distribution nor the connectivity of single nodes. We show that simulated annealing improves on the results previously obtained with a simple hill-climbing procedure. We also introduce a local move operator in order to facilitate actual rewiring and show numerically that the results are almost equally good.