LEIGH SALES, PRESENTER: The Dark Web is a mysterious part of the internet hidden to most computer users, but if you dig down, it's full of drug marketplaces selling everything imaginable and ready to ship at a moment's notice. The arrest of the founder of the notorious Silk Road website was supposed to shut the trade down. But instead, dozens of opportunistic competitors have sprung up to fill the space. One researcher says there's been at least a 30 per cent increase in the number of drug dealers and there are allegations that Australia Post is unwittingly becoming a drug courier. Conor Duffy reports.

CONOR DUFFY, REPORTER: In Brisbane's nightclub district, music lovers are queuing up to dance the night away. The Triffid is packed with thirsty fans and the bars are doing a good trade. But a growing number of young people are opting for an illegal high and they're sourcing it from darknet websites on the internet.

ANDREW MCMILLEN, MUSIC JOURNALIST & AUTHOR: A variety of substances, stimulants, psychedelics, like LSD, MDAMA, otherwise known as ecstasy in its pill form. I tried a variety of things.

CONOR DUFFY: Music journalist and author Andrew McMillen is no stranger to this secret online world and the drug parcels being delivered all over the country.

ANDREW MCMILLEN: They look like regular, non-descript, plain, white envelopes, the kind of thing where if you felt it, it felt like it had a couple of documents folded up. There's no way that you could tell just by feeling it or looking at it that inside was an illicit substance and that's by design of course.

CONOR DUFFY: Andrew McMillen has taken a break from using drugs, but he believes the darknet websites are still doing a booming trade.

ANDREW MCMILLEN: We're talking probably hundreds of letters per day, certainly on a weekly basis, you'd be looking at thousands of illicit substances being delivered through the Australian postal system, whether from international vendors or by domestic sellers here in Australia.

CONOR DUFFY: Using any illegal drugs is a risky and potentially fatal activity, but Andrew McMillen says the appeal of buying drugs online is the user rating system.

ANDREW MCMILLEN: The darknet markets have been a boon for people who care about safe, responsible usage because it's a peer-reviewed system.

NEWSREADER: 23-year-old James Monroe made a decision that would have fatal consequences.

CONOR DUFFY: Online drugs have claimed lives in Australia, including those sold from the first darknet marketplace, Silk Road.

ROSS ULBRICHT, SILK ROAD FOUNDER: I want you to be a part of it. You know, come live out here.

CONOR DUFFY: This man, Ross Ulbricht is now serving a life sentence for founding that online black market. He pitched it as a utopian dream, but ended up ordering murders to keep his network in place. The anonymous used on the Dark Web meant it took a huge multi-agency taskforce to bust Ulbricht and authorities hoped it would cruel the online drug market, but new operators are bigger than ever.

STEVE BRIGHT, CURTIN UNIVERSITY: So the market has actually fragmented, which means that if one of these new sites were to go down, if the people running one of these new sites were to be busted, there's a plethora of other sites that people are going to be able to continue to use.

CONOR DUFFY: In the two years since Silk Road was shut down, it's clear the dealers have bounced back. There are dozens of new drug markets and even a search engine for the Dark Web.

STEVE BRIGHT: One of the problems that we have now with the fragmentation of the marketplace is if you're looking for a particular substance or a particular vendor, you might have to go to different markets to find that product or find that vendor.

CONOR DUFFY: Australian drug dealers are brazenly selling everything from ice to ecstasy and pharmaceuticals. There's so many sellers, they have to compete to attract the attention of buyers.

STEVE BRIGHT: They use traditional marketing strategies, things like buy one, get one free, buying a gram of methamphetamine and getting 10 Diazepam. Or even traditional marketing things like fair trade cocaine or opium-free - sorry, conflict-free opium.

CONOR DUFFY: Drugs researcher Dr Steve Bright from Curtin University uses the number of sellers on darknet sites to measure the size or health of the market.

STEVE BRIGHT: There's been about a 30 to 50 per cent increase if you just look at the individual markets. However, if you were to add up all the new markets, of course that would be assuming that on every market there's different people selling, it would be much closer to a 100 or 200 per cent increase in the number of listings since Silk Road I initially went down.

CONOR DUFFY: Joe Van Buskirk from the National Drug and Alcohol Research Centre has noticed the new drug market functioning as it does on the street with dealers working to take out the competition.

JOE VAN BUSKIRK, NATIONAL DRUG & ALCOHOL RESEARCH CENTRE: The threats to the communities appear to be coming from both external factors, so law enforcement, as well as internal factors, so that's within the communities themselves, so that might be scams or hackers actively trying to bring down rival marketplaces.

CONOR DUFFY: The lead law enforcement agency for stopping darknet drugs is the Australian Customs and Border Service, which declined to be interviewed, but issued this statement to 7.30: "The key message for darknet illegal marketplace users is that you face the very real risk of a criminal record, possible jail time or losing all of your money if you choose to illegally purchase and import illicit goods."

But with new sites opening all the time, law enforcement will need to keep a constant eye on the secret cargo in the nation's postal system.

LEIGH SALES: Conor Duffy reporting.

Response to 7.30 by a spokesperson from Customs and Border Protection:

The Australian Customs and Border Protection Service (ACBPS) and other Australian law enforcement agencies are well aware of this method of drug importation and are committed to targeting and combating it. While it is not an offence to access websites such as Silk Road, it is an offence to import or attempt to import a border controlled drug into Australia from these websites.

The ACBPS works alongside our partner agencies on this matter, including the Australian Federal Police and state/territory police. This collaboration results in strategic targeting and increased interception of attempted illegal imports. It also creates a global web of intelligence about known sellers and buyers.

The fall of Silk Road in late 2013 marked the start of a significant period of volatility in the illicit darknet trade as a string of high profile darknet sites fell victim to either law enforcement activity, hacking or site operator fraud. In the case of several sites, including SHEEP and BMR, allegations soon emerged that site operators had shut down their marketplaces and stolen both buyer and seller Bitcoins held in escrow.

Other illicit darknet trade marketplaces which have sought to the fill the void left by the collapse of the larger sites have also failed or had major security breaches. This includes Silk Road 2.0 which in February 2014 lost millions of dollars in buyers and sellers Bitcoin after the site was hacked.

Darknet markets continue to be volatile and while the number of listings and marketplaces may have expanded, so too has the incidence of listings fraud, marketplace failures and Bitcoin losses. Where buyers and sellers previously had to fear being ripped off by each other, they now risk having their money stolen by people hosting their illegal trade activities.

Illegally importing any border controlled good is taken very seriously. In addition to the risk of being exploited by online dealers, consumers also risk the prospect of a serious fine and/or imprisonment.

The key message for darknet illegal marketplace users is that you face the very real risk of a criminal record, possible goal time or losing all of your money if you choose to illegally purchase and import illicit goods through darknet.