The Defense Department earlier this year fought off Russian hackers who accessed an unclassified network, Defense Secretary Ashton Carter said Thursday.Carter said the hackers discovered an old vulnerability in a legacy network that had been patched. Carter said DoD identified the compromise and had incident responders hunting down intruders within 24 hours. “I still worry about what we don’t know because this is only one attack we found,” Carter told an audience during a speech at Stanford University in Palo…
