Terrorists have been linked to the illegal internet trade of medical products, regulators said as they announced that more than £15 million of counterfeit and unlicensed medicines and devices have been seized in the UK.
The haul, which has not been linked to terrorism, is the biggest recorded to date and includes huge quantities of illegally supplied and potentially harmful slimming pills, erectile dysfunction tablets, anaemia pills and narcolepsy tablets.
Unlicensed foreign medicines and fake condoms were also among the items seized following the operation by the Medicines and Healthcare products Regulatory Agency (MHRA).
It resulted in 1,380 websites being shut down, and Mark Jackon, the MHRA's head of intelligence, said criminals are increasingly using social media to sell their illegal wares.
He said: "If you put something like, for example, Kamagra (Viagra) into Twitter, you will find tweets with embedded links to websites within it, so even though there's a limit to 140 characters, the criminal can still put - and fairly anonymously - put their link to their shop.
"There is no doubt social media provides fantastic span if you're trying to sell a product, whether legitimately or illegitimately, and equally it provides a great deal of anonymity if you are doing something illegal."
He said the MHRA was working with a range of different social media companies including Facebook, Twitter and YouTube.
Asked if terror groups could be involved, Alastair Jeffrey, head of enforcement at the MHRA, said there was evidence of this happening elsewhere in the world.
"We've seen recently some indications that there may be terrorist groups involved," he said. "It's not something that the UK is concerned about at the moment."
But he added: "Everything's on our radar.
"We are beginning to see more established criminal groups entering this space," he said. "Risk is low and the profits are very high.
"That's why we really need to concentrate it and raise awareness of the dangers."
He said sentencing guidelines pre-date the internet and have not been updated since 1967, "but things have moved on significantly, profit has moved on significantly".
He added: "It doesn't reflect the severity of the crime and it doesn't act necessarily as a deterrent."
The MHRA said its enforcement officers and police raided a number of addresses and seized almost 6.2 million doses of falsified, counterfeit and unlicensed medicines, 15,000 of which were medical devices with a total value of £15.8 million.
The international investigation, named Operation Pangea VIII, was co-ordinated through Interpol and concluded with a week of international raids this month that resulted in 156 arrests worldwide.
The crackdown yielded £51.6 million of items from 115 different countries globally.
The operation resulted in the closure of two internet domain names selling the illicit diet drug dinitrophenol (DNP), which killed Leeds University student Sarah Houston, 23, in September 2012.
Ms Houston, who suffered from bulimia, was found dead in her bedroom in the city after secretly taking the drug, which is used as a pesticide and classified as an illegal food.
The majority of the products seized in the UK originated from India, China, Hong Kong and Singapore.
Interpol said 115 countries were involved in what was the largest ever operation focusing on the illicit sale of medicines and medical devices via the internet, with the cooperation of 236 different agencies from police, customs and health regulatory authorities.
Mr Jeffrey added: "The MHRA are committed to tackling the illegal trade in medical products and have been working with counterparts across the globe to close down websites and social media sites illegally advertising and selling these products.
"Criminals involved in the supply of medical products have no interest in your health; it is simply your money they want. Buying medicines from unregulated internet sites can be risky – you are gambling with your health."
Interpol's executive director of police services Tim Morris said: "More and more people are using the internet to purchase everyday items, and criminals are taking advantage of this trend to deceive customers into buying fake and even dangerous medicines and medical products online, with no concern to the health risks this poses."
"Through strong collaboration between law enforcement, health agencies and internet and payment companies, Interpol's Operation Pangea VIII has made significant progress in protecting innocent consumers by shutting down illegitimate online pharmacies and seizing illegal and counterfeit pharmaceutical products."