A top defense official noted this week that a foreign intelligence service stole about 24,000 files from a US defense contractor, which is a dramatic illustration of the threat facing the Pentagon as it makes every effort to tighten computer security.

William Lynn, a Deputy Defense Secretary, said that theft as he unveiled a new Pentagon cybersecurity strategy that designates cyberspace as an "operational domain" like sea, air and land where U.S. forces will practice, train and prepare to defend against attacks.

He noted that the theft took place in March and it was reportedly carried out by a foreign intelligence service. The theft targeted documents at a defense contractor which relate to developing weapons systems and defense equipment. Lynn declined to detail which country stood behind attacks as well as what company was hit or what the files contained.

"It was 24,000 files, which is a lot," Lynn said. "But I don't think it's the largest we've seen."