WASHINGTON (AP) — The head of the National Security Agency says he is seriously concerned that the contractor who disclosed secret U.S. surveillance programs had access to key parts of the NSA network.

NSA Director Keith Alexander told senators Wednesday that he is not ready to say all computer system administrators should be in-house government employees. But he said the NSA will have to take a close look at how well it oversees contract employees and the checks and balances that are in place.