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An "underground" website famed for selling drugs and other illegal items has been targeted in a cyberattack.

It appears the site suffered from a Distributed Denial of Service (DDoS) attack over the course of Tuesday and Wednesday.

Silk Road is only accessible through Tor, a service which allows users to browse anonymously online.

Several US politicians have called for the marketplace to be shut down, without success.

DDoS attacks involve flooding a website with more traffic than it can handle, therefore knocking it offline.

After two days of intermittent service, Silk Road's administrators told users on Wednesday morning the site was back in action - but said they could not rule out further downtime.

"Silk Road is open and accessible," said the site's administrator, writing under the user name Dread Pirate Roberts.

"As soon as the attacker finds out, he will likely change his tactics and try to take the site down again.

"Hopefully he won't be able to, but time will tell."

Prior to the site's recovery, owners speculated that the attack had exposed deep-rooted vulnerabilities in the Tor network.

"It's looking more and more like a restructuring of the Tor software or even the Tor network will be required to mitigate the kind of attack we are under," one update read.

Tor is a channel for people wanting to route their online communications anonymously.

It has been used by activists to avoid censorship as well as those seeking anonymity for more nefarious reasons - leading it to be known as the "dark web".

Speculation has spread over possible motives for the attack - including the possibility that a competitor is looking to set up a rival site on the network.

Silk Road takes its name from the historic trade routes spanning across Europe, Asia and parts of Africa.

The website has gained a reputation as being an online black market, with illegal goods being sold openly.

Carnegie Mellon University estimated that over $1.22m (£786,183) worth of trading took place on the site every month.

Payments for goods are made with the virtual currency Bitcoin, making it hard to track users buying drugs.

However, one Australian man using the site to sell drugs was arrested in February.

In a statement, local police said the arrest proved they were "one step ahead" of criminals on online networks.