This graph kind of scares me: https://blockchain.info/pools
BTC Guild owns 30% of the mining power of the entire network.
I've just started learning how Bitcoin works, but if BTC Guild ever goes up to 50% or so it means that the person in charge of that site (or the address facing the block-chain) has effectively really good chance of getting 5 or even 6 confirmations in a row.
The BTC Guild owner could make a large payment to someone (say to buy a car). The car seller would wait 3-4 confirmations for assurance that the network has accepted it. But then, since the BTCGuild owner owns 50% or more power of the network, he/she could outpace the network after those 3-4 confirmations and essentially get the money back from his car (by double-spending).
This person would be able to make all sorts of payments and overwrite the blocks where the payments were made to get back their money!
What is the Bitcoin community doing to make sure this won't happen?
Thanks,
Luca
