In unveiling the Defense Department's new cyberwar strategy on Thursday during a speech at Stanford University, Defense Secretary Ash Carter sent a stern message to cyber adversaries: America's "preference for deterrence and our defensive posture doesn't diminish our willingness to use cyber options if necessary," reported Stanford News.

The 42-page strategy, for the first time publicly, lays out circumstances which would justify the deployment of cyberweapons against an attacker.

The strategy states: "As a matter of principle, the United States will seek to exhaust all network defense and law enforcement options to mitigate any potential cyberrisk to the U.S. homeland or U.S. interests before conducting a cyberspace operation.

"There may be times when the president or the secretary of defense may determine that it would be appropriate for the U.S. military to conduct cyberoperations to disrupt an adversary's military related networks or infrastructure so that the U.S. military can protect U.S. interests in an area of operations. For example, the United States military might use cyberoperations to terminate an ongoing conflict on U.S. terms, or to disrupt an adversary's military systems to prevent the use of force against U.S. interests ... If directed by the President of the Secretary of Defense, the U.S. military may conduct cyber operations to counter an imminent or on-going attack against the U.S. homeland or U.S. interests in cyberspace."

As The New York Times notes, that last phrase seems to permit pre-emptive cyber attacks.

A 6,200-strong Cyber Mission Force will be assembled, comprised of military, civilian and defense contractors, and 133 cyber protection and combat teams will be operating by 2018.

"These are the talented individuals who hunt down intruders, red-team our networks and perform the forensics that help keep our systems secure," Carter said.

The strategy named America's biggest adversaries in cyberspace as being China, Russia, Iran and North Korea, but non-state actors like the Islamic State group were also mentioned.

China, the strategy says, continues to engage in cyberespionage, stealing intellectual property from businesses in order to "benefit Chinese companies and undercut U.S. competitiveness."

Included is a small section detailing how the U.S. plans to continue to work with Beijing to bring greater understanding and transparency of the two nation's cyber missions to "reduce the risks of misperception and miscalculation."

And if U.S.-Russia military relations ever resume, the Defense Department will "seek to develop a military-to-military cyber dialogue" to "foster strategic stability in cyberspace."

While the Internet has been one of the most transformative technologies, Carter said it also makes it much easier for terrorists to learn how to build bombs, and that needs to be addressed.

"The same technologies we use to target cruise missiles and jam enemy air defenses can be used against our own forces - and they're now available to the highest bidder," he told the Stanford audience, adding that the "only way we can do this right" is by rebuilding the partnership between the Pentagon, Washington and Silicon Valley.

To help improve that relationship, the Pentagon plans to create a new "point of partnership" in Silicon Valley, called the Defense Innovation Unit X, reported Stanford News.

"The first-of-its-kind unit will be staffed by an elite team of active-duty and civilian personnel, plus key people from the Reserves, where some of our best technical talent resides," Carter said. The unit would look for breakthrough technologies and potentially help startups identify new ways to work with the military, according to Stanford News.