Bitcoin prices fell as much as 6% today, and are now back below $600 for the first time since May.

The drop was likely linked to an announcement from the U.S. Marshals that it would begin auctioning off Bitcoins seized in the FBI's investigation of Silk Road, the defunct online drug marketplace.

The agency said it was auctioning off more than 29,000 Bitcoins, worth nearly $18 million at Thursday prices. The amount remains a fraction of the 144,341 bitcoins now in the government's possession from the Silk Road case.

Elsewhere, Expedia announced it has begun accepting Bitcoin; and a Bitcoin mining company called HashPlex raised a seed round of $400,000 from a group of investors that included SecondMarket's Barry Silbert. The firm says it can run a user's Bitcoin mining software for them at a lower price.