This　paper　presents　an　attack　on　a　new　short　signature　scheme　from　bilinear　pairing　proposed　by　Dan　Boneh　et　al.　at　J.　Crypt.　We　show　that　an　attacker　can　alter　the　public　key　of　the　signer　and　then　can　forge　the　signer＇s　signature　for　any　message　m.　Furthermore,　we　argue　that　the　well-accepted　notion　of　security　for　signature　schemes,　namely　existential　unforgeability　against　adaptive　chosen-message　attacks,　is　not　adequate　for　the　multi-user　setting.　We　firstly　define　a　new　notion　of　security　named　non-repudiation　for　the　short　signature　schemes.　We　believe　that　the　signature　scheme,　which　satisfies　non-repudiation,　is　more　secure.　©　2009　IEEE.