One of the Dark Web's biggest marketplaces for illegal online trades was taken offline this week, with reports circulating that it was part of an 'exit scam'.

The AlphaBay marketplace had a user base of more than 20,000 users, whose unencrypted details have now been exposed as part of the shutdown.

Digital Shadows VP of strategy, Rick Holland, says that the site continued to release new features, including security enhancements.

"We confirmed that the site remained inaccessible at the time of writing. We detected only speculation as to why the marketplace was not accessible at the time of writing, with multiple users on Reddit suggesting an exit scam had taken place," Holland says.

Reports circulated that police raided two AlphaBay vendors' houses,, according to Holland.

Others have speculated that two large Bitcoin transactions to addresses belonging to AlphaBay owners were evidence of the owners stealing money - around US$3.8 million in Bitcoin.

Holland says there is no evidence of that claim yet. He says that exit scams, such as those suspected in the AlphaBay case, aren't new and are actually quite common.

"These exit scams are one of the risks when conducting business in criminal marketplaces. The increasing value of BTC (>$2,500 as of today) makes exit scams appealing. These exit scams are often the first assumption when a marketplace goes offline, however there are alternatives including intrusions from other criminals, DDoS attacks from competitors, law enforcement interdictions, and even unannounced site maintenance," he says.

"Multiple vendors of compromised data, payment card details, malware and other services would have to seek other online services. The Dream and Hansa markets are likely to benefit from any potential Alphabay demise. Digital Shadows is tracking this development and will provide updated analysis as it becomes available."