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Out of reach of regular internet searches is the secretive online world known as the 'dark web' - anonymous, virtually untraceable global networks used by political activists and criminals alike.

"You have the availability of multiple dealers so you can compare products - and customers can review the dealer's product, too."

American student, David - not his real name - explains why he chooses to buy illegal drugs on the so-called 'dark web'.

"You don't have to go in front of a street dealer, where there might be a risk of violence," he adds.

And it is not just drugs which are available on this online black market. Fake passports, guns - even child pornography.

Anonymous drug dealers

The dark web is facilitated by a global network of computer users who believe the internet should operate beyond the supervision of law enforcement agencies.

Media playback is unsupported on your device Media caption The BBC's 5 live Investigates team found class A drugs and guns for sale

It allows users like David, and those who sell him drugs, to remain anonymous. Users often do not know the real identity of the fellow users they are dealing with, and it is very difficult - although not impossible - for authorities to track them.

5 live Investigates spoke online with a number of anonymous dark web users.

One told the programme "I feel much safer [online] than doing transactions in the real world. I used to sell drugs in the real world. Nowadays I almost strictly use the dark web for any drug transaction."

Another said: "If you're young and trying to find a contact for drugs harder than marijuana it is practically impossible without risking exposure and arrest."

We don't have enough courts, we don't have enough judges, and we don't have enough police officers to tackle the real scale of illegal behaviour on the internet John Carr, Internet security adviser

Getting access to the dark web depends on users downloading freely available software, based on peer-to-peer file-sharing technology, which effectively scrambles the location of users and dark web websites.

It is not just a criminal domain, either - the dark web has proved a crucial tool in concealing the identity of political campaigners living in countries with oppressive governments.

It is said to have helped some of the organisers behind the Arab Spring protests.

That said, the potential for criminal enterprise is significant.

Researchers from the 5 live Investigates team successfully accessed the dark web, and made a purchase of the hallucinogen DMT - a class A drug, ranking it on a par with heroin and cocaine.

An extra layer of secrecy is added to the dark web by the use of Bitcoins - an electronic currency which is used legitimately by online gamers, but which can be used by criminals to mask their financial transactions.

After a wait of around 3 weeks a package arrived in the post with a Spanish postmark. Concealed between two thin strips of cardboard was a white powder.

Analytical Services International, at St George's University of London examined the drugs.

The lab test proved the powder was DMT - and that the dark web works.

We have no idea who sent the drugs to us. They have now been destroyed by the lab as possession of DMT can lead to a jail sentence of up to seven years.

Dealers of DMT can face a maximum life term in prison.

But what is being done to police the criminal activity that takes place on the dark web?

"Police officers on both sides of the Atlantic say the same thing," says John Carr, an internet security advisor to the British government and the United Nations.

Many people share the belief, myself included, that drugs should be legal and the dark web is that belief put into action 'David', Dark web user

"We don't have enough courts, we don't have enough judges, and we don't have enough police officers to tackle the real scale of illegal behaviour on the internet.

"What that means is increasingly we're going to have to look to technical solutions, we're going to have to look to the internet industry to help civil society deal with this really enormous problem the dark web has created," Mr Carr told the BBC.

"The police service is acutely aware of the large and growing problem of cybercrime and is actively working with police nationally and internationally along with the private sector in a bid to combat criminality on the web," says Deputy Assistant Commissioner Janet Williams, the lead on e-crime for the Association of Chief Police Officers.

Yet for all their efforts much of the illegal activity on the dark web remains beyond the reach of the police, and to some supporters of the dark web, its anonymity is its virtue.

They point to the protection it has offered to anti-government bloggers who spread the message of revolution during the Arab Spring.

And they argue that it continues to provide cover for dissidents who might otherwise face persecution in China.

For US student and dark web user David, it is about freedom of choice:

"Many people share the belief, myself included, that drugs should be legal and the dark web is that belief put into action."

You can listen to the full report on 5 live Investigates on Sunday, 5 February at 21:00 GMT on BBC 5 live.

Listen again via the 5 live website or by downloading the 5 live Investigates podcast.