"Those are legal questions that we are attempting to address," Miller said at a conference in Washington, adding that "there are certainly a lot of grey areas in this field".
He said hostile acts in cyberspace covered a wide range, from digital espionage to introducing false data into a network, that did not necessarily represent full-blown war.
But he said the threat to US networks from terrorists, criminals and others was real and growing.
The link for this article located at news24 is no longer available.