If you'd like an in-depth discussion of what Mt. Gox has screwed up and how: http://www.reddit.com/r/Bitcoin/comments/1x93tf/some_irc_chatter_about_what_is_goi

If you'd like an in-depth discussion of what Mt. Gox has screwed up and how: http://www.reddit.com/r/Bitcoin/comments/1x93tf/some_irc_chatter_about_what_is_going_on_at_mtgox/cf99yac http://www.reddit.com/r/Bitcoin/comments/1x93tf/some_irc_cha... They didn't discover anything - they were warned, quite some time ago, that they were not correctly spending and opening themselves up for double+ spends due to their own misunderstanding of how to reliably track a spend (compounded by their coding errors).