Media reports say Greek police on July 25 arrested a Russian man who allegedly masterminded a $4 billion money laundering scheme using the virtual currency bitcoins.

Alexander Vinnik, the head of the BTC bitcoin currency exchange, was reportedly arrested in a small beachside village in northern Greece, following an investigation led by the U.S. Justice Department along with several other federal agencies and task forces.

According to Reuters, U.S. officials alleged Vinnik and his firm "received" more than $4 billion in bitcoin and did substantial business in the United States without following appropriate protocols to protect against money laundering and other crimes.

U.S. authorities also linked him to the failure of Mt. Gox, a Japan-based bitcoin exchange that collapsed in 2014 after being hacked. Vinnik “obtained” funds from the hack of Mt. Gox and laundered them through BTC-e and Tradehill, another San Francisco-based exchange he owned, they said in the statement.

Reuters reports Vinnik’s arrest is the latest in a series of U.S. operations against Russian cyber criminals in Europe.  Last week, the U.S. Justice Department moved to shut down the dark web marketplace AlphaBay.

Bitcoin is a cryptocurrency and a digital payment system invented by an unknown programmer, or a group of programmers, under the name Satoshi Nakamoto.  It was released as open-source software in 2009.

The system is peer-to-peer, and transactions take place between users directly, without an intermediary.  These transactions are verified by network nodes and recorded in a public distributed ledger called a blockchain.  Since the system works without a central repository or single administrator, bitcoin is called the first decentralized digital currency.

Besides being created as a reward for mining, bitcoin can be exchanged for other currencies, products, and services in legal or black markets.

According to research produced by Cambridge University in 2017, there are 2.9 to 5.8 million unique users using a cryptocurrency wallet, most of them using bitcoin.

Unlike real-world money such as the U.S. dollar or euro, no central bank issues it and it is not guaranteed by any government.