The U.S. National Security Agency (NSA) is warning that Chinese-linked hacking groups are exploiting 25 vulnerabilities in software systems and network devices as part of cyberespionage campaigns - which means patching is urgent. NSA analysts say China-backed hackers are targeting the U.S. Defense Department as well as America's national security systems and the private defense industry, using vulnerabilities as launching pads into networks, according to the alert.