Amazon Smile, PayPal and credit card processors said no to the “alt-right” and other racist and white nationalists using their networks.

So, they turned to bitcoin, an online-only cryptocurrency not backed or used by any government.

The internet currency is a relatively recent invention.

Released publicly as open-source software in 2009 by an anonymous group, bitcoin doesn’t have a central bank or main agency policing it. Instead, a network of users conducts peer-to-peer transactions directly with the exchanges being verified by computer and logged publicly in what’s called a blockchain.

While the blockchain allows transactions to be tracked, it doesn’t give away the identities of either side of the transaction.

The University of Cambridge estimates that, in 2017, between 2.9 and 5.8 million unique users made use of cryptocurrency, with many using bitcoin.

And, bitcoins can be used to purchase all manner of goods and services and it can be used to make donations.

That’s primarily how the alt-right is using the cryptocurrency.

Websites such as WeSearchr, which raises money for a “bounty” for information, and Hatreon, where donations can be made to alt-right figures such as Andrew Anglin, primarily use bitcoin for fundraising.

Bitcoin purchases can be traced by a determined researcher. And, the Southern Poverty Law Center will be releasing a list of 200 accounts tied to white nationalists and racists in the coming week.

Forbes Magazine put bitcoin’s secrecy to the test by purchasing small amounts of marijuana online, then asking a researcher to see if she could figure out where the transactions originated.

She found the buys and traced it back to Forbes.

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