The clandestine online marketplace, Silk Road, has forfeited Bitcoins worth $28m (£18m), US prosecutors have said.
Prosecutors had seized the Bitcoins - a virtual currency - as they shut the website, which allowed users to trade in illegal drugs, last year.
The seized Bitcoins were allegedly used "to facilitate money laundering", the prosecutors claimed.
Bitcoins have gained popularity recently but there have been fears they may be used for illegal activities.
"We continue our efforts to take the profit out of crime and signal to those who would turn to the dark web for illicit activity that they have chosen the wrong path," US prosecutor Preet Bharara said in a statement.
Mr Bharara added that prosecutors were treating Bitcoins like any other asset involved in money laundering and criminal activity.
"These Bitcoins were forfeited not because they are Bitcoins, but because they were, as the court found, the proceeds of crimes," he said.
The US authorities have alleged that Silk Road had been designed to "enable its users to buy and sell illegal drugs and other unlawful goods and services anonymously".
They said they had also filed charges against Ross William Ulbricht, the alleged owner of the site.
Mr Ulbricht is also known as Dread Pirate Roberts, DPR and Silk Road, the prosecutors said.
As part of the action against the Mr Ulbricht, prosecutors said they had seized an additional 144,336 Bitcoins.
These are worth nearly $130m at current value.
Mr Ulbricht has filed a claim contesting the seizure of the Bitcoins, asserting that they were found on his personal computer and belong to him rather than Silk Road.