"Follow the money trail" has been the mantra of criminal investigators for generations.
In the cyber world, that battle between criminals and authorities has been raging for years.
Despite the anonymous nature of cryptocurrencies, dozens of cybercriminals have been caught in the past two years thanks to new techniques that can trace their funds across the cryptocurrency blockchain -- a public record of all transactions between bitcoin "wallets."
But could the situation be reversed now?
A new service has appeared on the darknet that offers criminals a way to check how "pure" their digital coins are.
"We're seeing criminals start to fight blockchain analytics and this service is the first to do that," explains Dr. Tom Robinson, chief scientist and founder of analytics firm Eliptic, which discovered the site.
"It's called Antianalysis and for three dollars, criminals can now check their bitcoin wallets and see if the authorities can see any connection to criminal activity," says Dr Robinson.
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Elliptik says the discovery shows how sophisticated cybercrime networks are becoming and how worried criminals are about being caught.
"It's a very useful technique. If your funds are tainted, you can launder them some more and try to remove that connection to criminal activity until you have clean coins," he says.
Dr. Robinson says it's a worrying new trend that could make their job and that of law enforcement more difficult.
But luckily, its researchers who tested it say the service isn't working very well at the moment.
“It's actually not very good at identifying links to criminal sites.
"However, it will inevitably improve over time. And that's why I think this will be a significant opportunity for criminals and money launderers in the future," he says.
Governments around the world, in China, the United Arab Emirates and Great Britain, are trying to deal with the growing problem of money laundering through cryptocurrencies.
There have been some major arrests thanks to cryptocurrency tracking - such as that of American teenager Graham Ivan Clark, who is currently in prison for masterminding one of the biggest social media hacks to date.
Clark found a way to take over the accounts of dozens of public figures on Twitter, including Kim Kardashian, Elon Musk, Bill Gates and Joe Biden.
Clark and his hacking team then tweeted an advertisement for the cryptocurrency scam, receiving hundreds of money transfers from people hoping to cash in on the fake sweepstakes.
In just a few hours, Clark made more than $100.000 and began the process of moving funds to cover the trail.
He failed.
In the indictment against him, the US Department of Justice stated that the officers successfully "analyzed the blockchain and de-anonymized the blockchain transactions which allowed the identification" of the hacker.
Clark, now 18, pleaded guilty and is serving a three-year sentence in a Florida prison.
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The growth of private coins
Another trend that worries the authorities is the increased use of so-called private coins.
These are cryptocurrencies like Monero and XRP that offer more anonymity than mainstream coins like Bitcoin.
In some extortion cases, hackers are now asking victims to pay using those coins in exchange for a discount.
Once again, this is a trend that has yet to fully catch on, and Kim Grauer, director of research at cryptocurrency analysis firm Chainanalysis, says this method has some downsides for criminals.
"Private coins have not yet developed to the extent one would expect.
"The primary reason is that they are not as liquid as Bitcoin and other cryptocurrencies."
"Cryptocurrency is only useful if you can buy goods and services or turn it into mainstream money, which is much harder to do with private coins."
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