Official US government statement: "When warranted, we will respond to hostile attacks in cyberspace as we would to any other threat to our country. We reserve the right to use all necessary means - diplomatic, informational, military and economic - to defend our nation, our allies, our partners and our interests."
The problem is attribution. If a cyber attack is traced to an IP address in Russia it's almost impossible to know for certain that it was really sponsored by the Russian government. It could have been some random kid in Australia who pwned a vulnerable computer in Russia and used it to launch an attack for the lulz.
Since deterrence is ineffective for cyber defense we need to put our focus into hardening critical systems.
https://www.reuters.com/article/idUSTRE7AF02Y/
The problem is attribution. If a cyber attack is traced to an IP address in Russia it's almost impossible to know for certain that it was really sponsored by the Russian government. It could have been some random kid in Australia who pwned a vulnerable computer in Russia and used it to launch an attack for the lulz.
Since deterrence is ineffective for cyber defense we need to put our focus into hardening critical systems.