To all of you people selecting more-is-always-better I challenge you to defend your irrational belief.  I suppose you would gladly spend 100% of your income on taxes to provide even more security for the banks.  A police man at every cash register and triple factor authentication on every transaction?    After all there appears to be no limit to how much you are willing to spend on 'security'.  

If you think it needs be be more than $100 M then post here with a number.  But to assume the sky is the limit is to avoid all rational economic calculation.  

What exactly the attack that one could profitably make against $10 million dollars worth of electricity invested in hash power?