jan ▁horse ▁affect ing ▁personal ▁computer ▁systems ▁running ▁Mac ▁OS ▁X . ▁The ▁first ▁variant ▁of ▁Flash back ▁was ▁discovered ▁by ▁ant iv irus ▁company ▁In te go ▁in ▁September ▁ 2 0 1 1 . ▁ ▁In fection ▁According ▁to ▁the ▁Russian ▁ant iv irus ▁company ▁Dr . ▁Web , ▁a ▁modified ▁version ▁of ▁the ▁" Back Do or . Fl ash back . 3 9 " ▁variant ▁of ▁the ▁Flash back ▁Tro jan ▁had ▁inf ected ▁over ▁ 6 0 0 , 0 0 0 ▁Mac ▁computers , ▁forming ▁a ▁bot net ▁that ▁included ▁ 2 7 4 ▁b ots ▁located ▁in ▁Cu pert ino , ▁California . ▁The ▁find ings ▁were ▁confirmed ▁one ▁day ▁later ▁by ▁another ▁computer ▁security ▁firm , ▁K asp ers ky ▁Lab . ▁This ▁variant ▁of ▁the ▁mal ware ▁was ▁first ▁detected ▁in ▁April ▁ 2 0 1 2 ▁by ▁Finland - based ▁computer ▁security ▁firm ▁F - Sec ure . ▁Dr . ▁Web ▁estimated ▁that ▁in ▁early ▁April ▁ 2 0 1 2 , ▁ 5 6 . 6 % ▁of ▁inf ected ▁computers ▁were ▁located ▁within ▁the ▁United ▁States , ▁ 1 9 . 8 % ▁in ▁Canada , ▁ 1 2 . 8 % ▁in ▁the ▁United ▁Kingdom ▁and ▁ 6 . 1 % ▁in ▁Australia . ▁ ▁Details ▁The ▁original ▁variant ▁used ▁a ▁fake ▁installer ▁of ▁Ad obe ▁Flash ▁Player ▁to ▁install ▁the ▁mal ware , ▁hence ▁the ▁name ▁" Fl ash back ". ▁ ▁A ▁later ▁variant ▁target ed ▁a ▁Java