A foreign intelligence service stole 24,000 files from a US defence contractor in March, Deputy Defence Secretary William Lynn said.
He disclosed the theft details on Thursday as he unveiled a new Pentagon cyber-security strategy that designates cyberspace as an operational domain like sea, air and land.
Mr Lynn said that the theft had targeted files at a defence contractor developing weapons systems and defence equipment. He would not give the name of the country he believes was behind the attack, or say what company was hit or what the files contained.
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