Ross William Ulbricht, known online as Dread Pirate Roberts, is shown in this courtroom sketch appearing before Federal Judge Joseph Spero in U.S. Federal Court in San Francisco, California, on Oct. 4, 2013.

British authorities say more arrests are coming. The method by which the U.S. arrests appear to have come about — routine package interdiction, then a simple investigation — suggests that other American dealers may be at risk. In addition, the charges aren't new or novel, but simple and very severe:

NOD, a well-known drug dealer on the defunct online black market Silk Road, has been arrested in Washington State, along with a partner. Across the Atlantic, four Silk Road users were arrested by British authorities "on suspicion of supplying controlled drugs." In Sweden, two Silk Road users have been arrested for allegedly selling marijuana on the site.

"Based on the forgoing," the complaint says, "I submit that there is probably cause to believe that STEVEN SADLER and JENNA WHITE have conspired to distribute cocaine, heroin, and methamphetamine."

Nothing about this series of arrests, or last week's criminal complaint against Silk Road's proprietor, should be comforting to Silk Road dealers. Investigators seem to have caught on to Silk Road about as fast as users did.

And those users are getting worried too. "Got a call..." writes one user on Reddit. "Apparently I have to meet with the local police agency. Is this a true law in the states that I have to go?" Many other users seem to be named, or at least identified by address, in the complaint against Sadler and White; if authorities were interested in prosecuting their customers, they have a lot of information to work with.

A user on the encrypted Silk Road forums claiming to be one of the sellers targeted in the UK investigation has a rosier outlook. "I'm the one arrested in Devon, anyone know who the others are?" asks the user, who says he is popular Silk Road user PlutoPete. "Unlike other vendors, my address was no secret, PlanetPluto is a registered business selling legal products. I break a few small rules such as selling seeds together with a growguide, but they would look so pathetic doing me for stuff like that the publicity would just send me more customers," he wrote on Oct. 4, soon after British authorities seized his "legal herbs" (Salvia, Kratom) and computers.

"They got the warrant on the suspicion that i'm involved in the large scale distribution of class A drugs, my lawyer says there's no way they could suspect that from the evidence that had been disclosed to that point, but that was before i returned home and found the copy of the evidence list, 18 pages of stuff they've seized," he writes.

Regardless, this will send a shock through the so-called dark net. Feds are going after Silk Road like a simple drug ring, not an exotic website, and have been investigating it effectively since 2011.

The relative difficulty of accessing Silk Road — setting up Tor, converting cash to Bitcoins, setting up encrypted communications — may have given users a sense of security and secrecy. But these technological safeguards aren't really safeguards at all: Buying and selling illegal substances through a service run by the government, it turns out, is more than enough to get you caught.