. ▁At ▁ 1 2 : 2 0 pm , ▁all ▁trad ing ▁was ▁halt ed ▁on ▁the ▁Nas da q ▁exchange . ▁There ▁was ▁a ▁subsequent ▁trad ing ▁halt ▁placed ▁on ▁‘ T ape ▁C ’ ▁stock s ▁- ▁Nas da q ▁listed ▁stock s ▁which ▁may ▁be ▁trad ed ▁on ▁other ▁ex changes , ▁as ▁quotes ▁could ▁not ▁be ▁provided ▁for ▁those ▁se cur ities . ▁Un like ▁some ▁purpose ful ▁trad ing ▁hal ts , ▁options ▁trad ing ▁did ▁not ▁continue ▁during ▁the ▁flash ▁free ze . ▁In ▁a ▁statement , ▁Nas da q ▁claimed ▁that ▁the ▁initial ▁cause ▁of ▁the ▁out age ▁was ▁identified ▁and ▁resolved ▁within ▁ 3 0 ▁minutes ▁and ▁that ▁the ▁additional ▁out age ▁time ▁was ▁to ▁ensure ▁that ▁there ▁would ▁be ▁a ▁stable ▁re open ing ▁of ▁the ▁market . ▁ ▁Test ▁tr ades ▁began ▁at ▁ 2 : 4 5 pm ▁and ▁trad ing ▁officially ▁res umed ▁at ▁ 3 : 2 5 pm . ▁It ▁was ▁later ▁reported ▁that ▁tr ades ▁in ▁‘ dark ▁po ols ’ ▁on ▁Nas da q ▁listed ▁se cur ities ▁continued ▁in ▁a ▁limited ▁manner ▁past ▁ 1 2 : 1 4 pm ▁when ▁trad ing ▁was ▁halt ed , ▁until ▁approximately ▁ 1 : 1 5 pm . ▁ ▁Multiple ▁" dark ▁pool " ▁trad ing ▁platforms ▁were ▁also ▁shut ▁down ▁during ▁the ▁free ze , ▁and ▁some ▁did ▁not ▁re open ▁until ▁the ▁follow ▁day , ▁such ▁as ▁S igma ▁X , ▁a ▁dark ▁pool ▁operated