4 , ▁C yl ance ▁Inc . ▁published ▁an ▁investigation ▁on ▁so - called ▁" Operation ▁Cle aver " ▁which ▁target ed ▁over ▁ 5 0 ▁world ' s ▁un named ▁leading ▁enter pr ises , ▁including ▁in ▁United ▁States . ▁Federal ▁Bureau ▁of ▁Investig ation ▁t ac it ly ▁acknowled ged ▁the ▁operation ▁and ▁" warn ed ▁business es ▁to ▁stay ▁vig il ant ▁and ▁to ▁report ▁any ▁susp icious ▁activity ▁sp otted ▁on ▁the ▁companies ' ▁computer ▁systems ". ▁ ▁In ▁December ▁ 2 0 1 4 , ▁in ▁response ▁to ▁a ▁hack ▁on ▁the ▁US ▁based ▁company ▁Sony ▁( see ▁Sony ▁Pictures ▁hack ) ▁believed ▁to ▁be ▁perpet r ated ▁by ▁North ▁Korea , ▁the ▁US ▁government ▁created ▁new ▁economic ▁san ctions ▁on ▁North ▁Korea ▁and ▁listed ▁the ▁country ▁as ▁a ▁state ▁spons or ▁of ▁terror ism . ▁After ▁the ▁hack , ▁there ▁was ▁an ▁internet ▁black out ▁over ▁most ▁of ▁North ▁Korea ▁alleg edly ▁caused ▁by ▁the ▁US , ▁but ▁there ▁was ▁no ▁definit ive ▁evidence ▁to ▁support ▁that ▁claim . ▁ ▁In ▁April ▁ 2 0 1 5 , ▁The ▁Department ▁of ▁Def ense ▁Cy ber ▁Str ategy ▁was ▁updated ▁and ▁published . ▁ ▁Original ▁Do D ▁Str ategy ▁for ▁Oper ating ▁In ▁Cy bers pace ▁was ▁published ▁in ▁July ▁ 2 0 1 1 . ▁ ▁In ▁ 2 0 1 5 ▁the ▁United ▁States ▁Office ▁of ▁Person nel ▁Management ▁( OP M ) ▁was ▁victim ▁to ▁what ▁has ▁been ▁described ▁by ▁federal ▁officials ▁as ▁among ▁the