Unknown attackers have been testing the defenses of companies that run critical parts of the Internet, possibly to figure out how to take them down, cybersecurity expert Bruce Schneier warned Tuesday. Large nation states -- perhaps China or Russia -- are the likely culprits, he suggested. "Nation state actors are going to probe to find weaknesses in all of our technologies," said Travis Smith, senior security research engineer at Tripwire. They "want to know what can be done not only in the event of a cyberwar but a kinetic war as well."