Business Insider has the details:
“The FBI has not been able to get to Ulbricht’s personal Bitcoin yet,” wrote Hill. An FBI spokesperson said to Hill that the “$80m worth” that Ulbricht had “was held separately and is encrypted”. At current exchange rates, that represents slightly more than 5% of all bitcoins in circulation.
Even if the FBI is not able to transfer the money, merely having possession of the wallet file itself is enough to prevent the coins being spent. The Bureau is in a position equivalent to having seized a safe belonging to a suspect with no idea of the combination – and no hope of forcing it open any other way.
The Guardian has a piece containing general information about Bitcoins.
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