Hmm, from what I saw, Blockchain keeps everything encrypted at all times, so it looks pretty secure. I imagine that buying Bitcoins might be more problematic, though, true.
Inject into their code and wait until the big players log in and reveal their keys to the trusted site. Game over. The encryption only protects against an opportunistic database grab.
Well it's different, but the end result is the same.
Banks are massive and have pretty much everything insured. If they mess up, it's on them. Not so much with bitcoin, if they mess up their users lose out.
Additionally demonstrated by Mt. Gox, most bitcoin services are run by complete novices. Basic SQL injection on a website dealing with currency is unforgivable.
