The Pentagon announced recently in its first formal cyber strategy that cyber attacks constitute an act of war — and could merit a traditional military response.
Never mind the problem of attributing cyber attacks to a single, definitive source; even if the perpetrators can be traced to a specific country, the hackers in question may not be working for the state in which they reside. In cyber warfare, it is easy for states to claim plausible deniability.
This kind of deterrence doesn’t work. What is needed is appropriate security infrastructure and, in extreme cases, a carefully measured response. Of course, given US military’s track record of invading two countries to catch a guy who was in neither, this is not really their style.