The anonymous online marketplace Silk Road 2 says it has been hacked resulting in the loss of all its customers' bitcoins.
An administrator for the site said hackers had manipulated computer code enabling them to withdraw $2.7m (£1.6m) worth of the virtual currency.
It follows similar attacks on two exchanges that trade in bitcoins earlier in the week.
Silk Road 2 is known for selling drugs and other illegal items.
The site is only accessible through Tor, a network that allows users to browse anonymously online. The virtual currency Bitcoin is often used in transactions as it also grants users a degree of anonymity.
The original Silk Road site was shut down by the FBI in 2013 but those behind it said they would start a new site and shortly afterwards Silk Road 2 appeared online.
Completely empty
In a statement posted on Silk Road 2 forums, the administrator of the site, known as Defcon, said: "We have been hacked."
"Nobody is in danger, no information has been leaked, and server access was never obtained by the attacker.
"Our initial investigations indicate that a vendor exploited a recently discovered vulnerability in the Bitcoin protocol known as "transaction malleability" to repeatedly withdraw coins from our system until it was completely empty," he said.
http://www.bbc.co.uk/news/technology-26187725