one of the largest attacks to date in march. >> this was significant and it was a defense contractor. data related to systems developed at the department of defense. large, 24,000 files. it was done by we think foreign intelligence service. >> reporter: lynn refused to say which nation but privately pentagon officials concede most prior attacks emanated from russia or china. in may, lockheed martin the largest defense department contractor and maker of the super stealth next generation s-35 joint strike fighter revealed that its computers had been hacked. how will the u.s. military respond to future attacks? >> the president and the congress would treat it as an act of war and respond accordingly. >> reporter: experts say the cyber strategy needs work. >> there has to be an offensive piece of the strategy. there are times we have to use