A TV grab handout by Spanish Policia Nacional shows two police officers detaining the Liberty Reserve founder Arthur Budovsky in Barajas airport, Madrid, Spain, on May 28, 2013. Budovsky, who set up digital currency business, is held as part of money-laundering investigation involving the US. (HO/SPANISH POLICIA NACIONAL/EPA)

Federal prosecutors charged seven men in connection with a massive online money-laundering operation that for years offered a way for drug traffickers, child pornographers and others in the criminal underworld to move cash around the world quickly, officials said Tuesday.

The network, run by a Costa Rican company called Liberty Reserve, processed at least $6 billion for more than a million clients, including 200,000 in the United States. Federal officials accused the company’s founder, Arthur Budovsky, of setting up a “bank of choice” for criminals that became one of the largest laundering operations in history.

The investigation involved law enforcement officials from 17 countries, highlighting the increasingly complex nature of illicit financing systems that have gone not only global but virtual as well. Anyone could open an online account with Liberty Reserve from anywhere in the world, without providing identification, and then deposit or transfer money to others with accounts.

In lieu of their real names, some used monikers such as “Russia Hackers” or “Hacker Account,” said federal prosecutors in the Southern District of New York.

The move against Liberty Reserve marks an escalation of the scrutiny of the rapidly evolving world of online finance. Federal officials were able to shutter the Liberty Reserve network largely because it was operated by one firm. But a new generation of decentralized payment networks may prove a greater challenge for U.S. authorities.

The most popular of these is Bitcoin, an online currency that is traded by thousands of users on several exchanges worldwide. No single company is in charge of the network. Because consumers can remain anonymous, it has grown popular among legitimate and criminal elements alike, analysts said. Anyone can buy and sell Bitcoins, or transmit them to others, without providing identification.

That sprawling, decentralized network could create a quandary for federal regulators. Bitcoin doesn’t fit well into existing laws against money-laundering, which assume the existence of an operator who can be compelled to implement regulations.

Two weeks ago, authorities went after one Bitcoin exchange, seizing money from Mt. Gox, a leading exchange based in Japan. Like Liberty Reserve, Mt. Gox was targeted for not complying with U.S. laws against money-laundering. That action had little effect on the broader Bitcoin network.

Acting Assistant Attorney General Mythili Raman declined to comment on whether the government has ongoing investigations involving Bitcoin or other electronic currencies. But she said that “other virtual payment systems should take notice of today’s announcement and ensure that they comply with . . . regulatory obligations and ensure they are not designed to be a safe haven for criminals to launder their criminal proceeds.”

The privacy offered by Bitcoin has attracted users with illicit intentions. For example, the online marketplace Silk Road allows users to buy drugs and other illegal goods with Bitcoins.

Bitcoin also has legitimate uses. Jerry Brito, a researcher at the Mercatus Center at George Mason University, points to a company called BitPay, which accepts Bitcoin payments on behalf of more than 5,000 legitimate merchants. BitPay processed $5.2 million in transactions in March, which the firm estimates was larger than the volume of illicit Silk Road transactions that month.

“Bitcoin is an ecosystem with licit and illicit uses,” Brito said. “The licit uses are beginning to outpace illicit uses.”

Leaders in the Bitcoin community said they have tried to stay within the bounds of the law. “If the U.S. government decided that Bitcoin was a bad thing and told me, ‘Stop doing what you’re doing,’ I’d stop doing what I’m doing,” Gavin Andresen, Bitcoin’s lead developer, told the New Yorker in a recent interview.

In contrast, federal prosecutors said Liberty Reserve was designed for illegal activities. “Liberty Reserve has become a financial hub of the cyber-crime world, facilitating a broad range of online criminal activity,” the federal indictment states.

Budovsky has a history of building money-transfer businesses that attract attention from federal regulators. In 2006, he faced charges relating to another money-transmission business, called Gold Age, that authorities said had not complied with regulations against money-laundering. He was convicted and sentenced to five years of probation.

Undeterred, Budovsky moved to Costa Rica, renounced his U.S. citizenship and founded Liberty Reserve. When the business came under scrutiny from Costa Rican regulators, Budovsky told them he had ceased operations in Costa Rica. In reality, U.S. prosecutors alleged, he continued operating it through shell companies.

Federal officials said the system enabled criminals to sell stolen credit card data and hacking software to one another — or transfer ill-gotten gain. Eight New Yorkers who recently were indicted on charges of stealing as much as $45 million from ATMs worldwide allegedly used Liberty Reserve to distribute their cash.

Budovsky, who was arrested in Spain over the weekend, could not be reached to comment. On Tuesday, Liberty Reserve’s Web site displayed a message saying it had been seized by federal officials.