▁an ▁information ▁security ▁design ation ▁used ▁by ▁some ▁govern ments . ▁ ▁United ▁States ▁Among ▁U . S .   g overn ment ▁information , ▁FO U O ▁is ▁primarily ▁used ▁by ▁the ▁U . S .   Dep art ment ▁of ▁Def ense ▁as ▁a ▁handling ▁instruction ▁for ▁Control led ▁Un class ified ▁Information ▁( C UI ) ▁which ▁may ▁be ▁ex empt ▁from ▁release ▁under ▁exem ptions ▁two ▁through ▁nine ▁of ▁the ▁Fre edom ▁of ▁Information ▁Act ▁( FO IA ). ▁It ▁is ▁one ▁of ▁the ▁various ▁sub - c ategor izations ▁for ▁strictly ▁un class ified ▁information ▁which , ▁on ▁ 2 4 ▁February ▁ 2 0 1 2 , ▁was ▁officially ▁cons olid ated ▁as ▁C UI . ▁Other ▁depart ments ▁using ▁this ▁design ation ▁include ▁the ▁Department ▁of ▁Hom eland ▁Security . ▁ ▁U . S . ▁Department ▁of ▁Def ense ▁On ▁ 2 4 ▁February ▁ 2 0 1 2 , ▁the ▁Under ▁Secretary ▁of ▁Def ense ▁for ▁Int elligence ▁published ▁the ▁public ly ▁available ▁Do DM ▁ 5 2 0 0 . 0 1 , ▁a ▁four - volume ▁manual ▁cons olid ating ▁all ▁mark ing ▁of ▁information ▁used ▁by ▁the ▁U . S .   Dep art ment ▁of ▁Def ense . ▁There ▁is ▁a ▁lot ▁more ▁information ▁on ▁the ▁mark ing , ▁access , ▁and ▁protection ▁of ▁" For ▁Official ▁Use ▁Only " ▁information . ▁Most ▁of ▁the ▁information ▁is ▁in ▁the ▁fourth ▁volume , ▁but ▁the ▁second ▁volume ▁also ▁contains ▁gu idel ines