The value of Bitcoin has soared this week after the virtual currency was described as "legitimate" by a Senate hearing.
It rose to over $900 (£559) as the Homeland Security and Governmental Affairs Committee revealed it is investigating the currency.
Bitcoin has now more than trebled in value since October and the chair of the committee, Senator Thomas Carper, noted how the virtual currency has "captured the imagination of some, struck fear among others, and confused the heck out of the rest of us".
It gained fame after being linked to the Silk Road website, which sold illegal goods such as drugs via bitcoin. The site was recently closed down by the FBI.
The FBI said in a letter to the Senate hearing that bitcoin is a "legitimate" currency, although it could be "exploited by malicious actors".
Bitcoin's value has been steadily increasing for much of the year, but the virtual currency lost half of its value in 24 hours back in April as panic buying affected its main exchange MTGox.
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