I see from the posts that a number of people haven't cottoned on to the core issue.

Step one: with borrowed money, buy 40% of the coins.
Step two: sell all the coins, pay back the loan, banking any profits or covering any loss.
Step three: mount continuous, free, penalty-less attacks for evermore.

51% is the minimum for a statistically-guaranteed success. At 40% success isn't guaranteed but those are terrific odds when you can mount a permanent attack basically for free. The odds get more forbidding at 20%, obviously --- but when paired with infinite free attacks, that's still quite tempting, kinda like a CDO Tier3.

That's my understanding of the vulnerability anyway --- I am open to correction.

Cheers,

Graham


Edit: explicitly added openness to correction