In the 18 months since the Silk Road online black market for narcotics was taken down by a swarm of three-letter agencies, a site known as Evolution has taken its place at the top of the dark web drug trade. Now Evolution, too, has suddenly dropped off the face of the internet. But unlike its Silk Road predecessor, there's no indication that law enforcement took down the newer black market. Instead, it's simply, mysteriously vanished—with rumors swirling that its own administrators may have run off with many millions of dollars of its users' drug money.

Over the past weekend, the massive anonymous market known as Evolution halted withdrawals of bitcoin from its website, telling users that it was dealing with technical difficulties. Then on Tuesday evening, both its market and user forum went offline, with no opportunity for drug buyers and sellers to pull out the funds they had stored in their Evolution accounts. The result has been a wave of panic that's shaken the online black market economy as much as any of the law enforcement drug busts of the last two years.

Late Tuesday, a Reddit user named NSWGreat who had earlier self-described as an Evolution drug dealer and "public relations" staffer —he or she had even hosted an "ask me anything" session about the job days earlier—wrote a post to Reddit's darknet markets forum that claimed to confirm Evolution's administrators had in fact shut down the site's back end too, and escaped with users' money; NSWGreat described confronting Evolution's two pseudonymous owners, Verto and Kimble, who he or she says then admitted they were closing the market and stealing its funds. "I am so sorry, but Verto and Kimble have f–ked us all. I have over $20,000 in escrow myself from sales," NSWGreat wrote. "I'm sorry for everyone's loses, I'm gutted and speechless. I feel so betrayed."

"Don't do this to us Evo staff please," another user pleaded in a response on Reddit. "I owe money and I can't pay if this is true. My lifes in danger. Please don't be true please."

If Evolution's owners did in fact steal their users' funds stored on the site—a theory that's still not confirmed—it's not clear just how much they would have profited. But given the size of Evolution's market, with nearly 20,000 drug product listings as well as thousands more items ranging from weapons to stolen credit cards, the sum could easily be millions or even tens of millions of dollars worth of bitcoin. For comparison, the FBI seized $3.6 million worth of bitcoin from the original Silk Road at the time of its October 2013 takedown, when the site was still significantly smaller than Evolution.

For other dark web markets, technical glitches and long downtime would be routine, rather than a sign of a major scam. But since it first appeared online just over a year ago, Evolution had developed a reputation for professionalism and reliability. According to the site Dark Net Stats, the site had a 97% uptime rate, far higher than competing markets like Agora or the now-defunct Silk Road 2. The site gained users' trust by offering a feature known as "multi-signature transactions," designed to prevent exactly the sort of bitcoin theft its administrators are now accused of. (That system, would require at least two out of three parties in a transaction—the buyer, the seller, and Evolution's administrators—to sign off on a deal. But due to its complexity, buyers rarely used the feature.) That relative sophistication, along with the seizure of several smaller competitors in a string of law enforcement busts late last year, contributed to Evolution's rising position over the last year as the go-to online black market.

But Evolution also distinguished itself from other markets by its far looser sense of morality. While other sites followed the original Silk Road's ethos of selling only victimless contraband, Evolution also trafficked in stolen identity information. Its founder known as Verto had previously run a site known as the Tor Carder Forum, another invite-only dark web site devoted exclusively to credit card fraud. Given that criminal mindset, it may be no surprise that the site's owners might have eventually become willing to steal from their own users, too. As one user wrote on Reddit's dark net market forum, "[I'm] really... surprised Evo went out like this, but I mean from former carders and fraudsters; would you expect anything less?"

Others pointed out that competing black markets like Agora, which briefly held the top spot as the most popular dark web market before Evolution, will likely absorb the refugees from Evolution's vanished market. But even so, the Evolution staffers' theft of millions of dollars from their users—if it's confirmed—would put a temporary but serious dent in the internet's underground drug economy. "I am guessing [Evolution's owners] have new identities and a nice remote beachside mansion all lined up, probably there already," one user wrote on Reddit. "Damn, sounds like a movie, except real people lost real money."