Interesting, so how did you detect that there was a serious problem? Just by code inspection, or did you see a clash on randomly created addresses?
That would be gray hat. I am white hat.
I had the opportunity to take all of the money johoe did significantly before he even realized it was an issue. It wasn't my place to go saving anybodies coins, it was if anybodies it was blockchain.info's. I don't know the legality of what joehoe did, as far as I could justify in my head at the time even though it was a "good" act, it would still be breaking my countries law. During the event I asked blockchain.info for permission to sweep the money and return it to the company, but they didn't respond in time.
I'm not sure about the legality, but it was the only way to save the money. I didn't break into other computers; I just took the public ledger and extracted the private keys from that. Usually, if there is a problem with repeated R values, it is exploited within a few hours. In this case it took a bit more than 24 hours.
I wonder why you didn't sweep the remaining coins that required to break the RNG. When I did this after six days, I was astonished how much money there still was on these addresses.
This is important.
Please refrain from giving a step by step instruction on how to hack people's addresses.
I highly respect what johoe did but I think he got carried away with his new 'fame' by telling everybody how he did it.
Not cool.
I think, I never gave a step by step instruction of how to break an address. You are probably referring to the posting how to break a particular address using a particular chain of R values and other addresses. That description showed how I broke one particular key, but that key didn't have any money anyway. I didn't include the details, or any of the private keys. Of course, you can look up the details at Wikipedia. Or you can find the other step-by-step instructions on the web. The knowledge that it is possible to follow R values over several addresses was already out; there was another thread that started two weeks earlier. Also my posting was at a time when there were already bots sweeping the addresses when they were exploited. I tried to keep the details of the RNG secret as long as possible.