Drugs and guns are being sold in Scotland using a Russian messaging service, similar to WhatsApp.
Crooks and extremist groups have been drawn to use Telegram because end-to-end encryption guarantees no one else can see what's being said.
The site has become an essential communication tool for soldiers and civilians caught up in the Ukrainian war, and was set up by a dubbed "the Mark Zuckerberg of Russia".
But criminals not wanting to miss an opportunity to peddle their wares, are using it to their own corrupt advantage, a Sunday Mail investigation has revealed.
Police and officials say they are working to stop the trade after learning that dangerous contraband is being bought and distributed across the country by postal staff.
But a leading politician and drug campaigner has warned it's like "trying to stop the tide with your fingers".
On one group, Scotland Black Market, dealers sell everything from opiates to semi-automatic guns and official documents including fake money.
Drugs pushed include ecstasy and powerful liquid opiates like Farmapran, linked to Mexican drug cartels, and anti-histamine drug Promethazine, which is used to make a drug cocktail dubbed Sizzurp by US users.
Cannabis and edible versions of the drug is also sold, with minimum orders for 100g costing £420.
Organisers, who share pictures of what they are selling with the channel's nearly 9,000 subscribers, posted the rules and wrote: "Send me a picture of what you need.
"Send me your delivery details. Do payments (Bitcoin or iTunes giftcards). Patiently wait for your package to be delivered as fast as possible."
Other posts include boasts they can supply pistols, semi-automatic rifles and ammo.
Guns on offer include the Glock 30 Gen4.
Piles of £20 Bank of England banknotes are also pictured and offered on the site.
Other posts include Royal Mail tracking receipts for packages handed over in post offices from January where dealers promise the system is "safe and discreet".
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Desperate users can get same-day delivery for an added cost.
Glasgow MSP Paul Sweeney said: "The ability to intercept and stop drug, weapon and fake documents being sold via apps like Telegram is becoming increasingly hard to stop.
"It's like trying to stop the tide with your fingers."
On Dundee Kush Hut, 4366 subscribers are promised "top-shelf cannabis bud and edibles anywhere within Dundee and have it delivered to you at your doorstep".
Edinburgh Kush Hut also has dealers pushing super-powerful cannabis, skunk and hash.
Edinburgh University Professor Susan McKie, who has studied how dealers use Royal Mail, said: "Drug dealers have diversified how they operate in the last decade and this is part of that - using crypto-currency and even iTunes giftcards to avoid detection.
"It's not surprising that these platforms are also being used to sell other illegal contrabands.
"When we looked at the drugs that were intercepted, three-quarters of the parcels were large enough to suggest they were being used to buy wholesale before selling it on.
"As soon as one group shuts, another two spring up."
Dodgy groups our undercover reporters had been members of have been shut but new ones were still springing up last week.
The Post Office said it had tipped off police about suspicious packages, including £25,000 worth of cocaine seized last year and destined for Dingwall.
A spokesman added: "Postmasters and staff follow processes set by Royal Mail and ask customers if what they're sending contains prohibited items."
Detective Superintendent Craig Willison said: "We are aware websites and online platforms are used to sell illegal firearms and drugs. Any cases we identify or are made aware of will be thoroughly investigated."
A Royal Mail spokesperson said: "We work closely with the police and Border Force to help stop the carriage and delivery of illegal drugs.
"This includes X-ray screening of suspicious items, and sniffer dog deployment.
"We also encourage our postmen and women to report to their managers any suspicious items, which we then promptly refer to the authorities."
Telegram were contacted but did not respond.
