The federal government bureaucracy FinCEN, which comes up with rules and punishments regarding finances in the US recently addressed bitcoin. According to the government, bitcoin is legal to use. There is a separate rule for those who mine bitcoins: If they want to convert any bitcoins they mined into Federal Reserve Notes (US Government money), then they may have to register as Money Transfer Businesses. This is a process which involves applying for an government license which costs millions of dollars. The edict is absolutely unenforceable and will not be taken seriously. It could possibly mean more regulations for exchanges who wish to comply.
What all of this means beneath the surface is that the government is aware of bitcoin. It has chosen, for the moment, not to attack with any teeth, but to begin moderate intrusion into those who willingly comply.
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