Has the U.S. struck back in cyberwar?

North Korea’s internet has been shut down.  The suspicion is that the American government has struck back in retaliation for North Korea’s hack and extortion of Sony. From North Korea’s Internet collapses; U.S. declines to say if it’s responsible – World Israel News | Haaretz:

North Korea experienced sweeping and progressively worse Internet outages extending into Monday, with one computer expert saying the country’s online access is “totally down.” The White House and the State Department declined to say whether the U.S. government was responsible.

Early morning on Tuesday, it was reported that some N. Korea Internet services, including official KCNA news agency, were back up. “The question for the next few hours is whether it will return to the unstable fluctuations we saw before the outage,” Jim Cowie, chief scientist for the U.S.-based internet monitoring company Dyn, said.

President Barack Obama said Friday the U.S. government expected to respond to the hacking of Sony Pictures Entertainment Inc., which he described as an expensive act of “cyber vandalism” that he blamed on North Korea. Obama did not say how the U.S. might respond, and it was not immediately clear if the Internet connectivity problems represented the retribution. The U.S. government regards its offensive cyber operations as highly classified.

“We aren’t going to discuss, you know, publicly operational details about the possible response options or comment on those kind of reports in anyway except to say that as we implement our responses, some will be seen, some may not be seen,” State Department spokeswoman Marie Harf said.