NEW : Attack traced to the National Police Agency address in North Korea , officials say . China has staged similar attacks in the past , expert says . Banks , broadcasters targeted ; government networks unaffected , North Korea reports . Wednesday 's attack is consistent with what North Korea has done in the past , said Adam Segal , a cybersecurity expert with the Council on Foreign Relations . South Koreans military steps up its cyberdefense efforts in response .
NEW : Attack traced to the National Police Agency address in North Korea , officials say . China has staged similar attacks in the past , expert says . Banks , broadcasters targeted ; government networks unaffected , North Korea reports . South Koreans military steps up its cyberdefense efforts in response .