The exchange Mt. Gox was hacked multiple times with over 850,000 Bitcoin stolen.
Mt. Gox was the largest Bitcoin exchange, being responsible for over 80% of all trades at its time.
I have found these private chat logs, which were linked to in an ancient Reddit thread, the link was no longer working but I have found an archieved version of it.
All this chat has gone over Skype, which itself had some weaknesses and that time and was apparently used by them to share confidential information (never seen any media outlet reporting on that)
This look into Mt. Gox at one of its first hacks perfectly shows that they were doomed from the very beginning