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It turns out the conspiracy theorists were onto something. Classified documents provided by whistleblower Edward Snowden show that the National Security Agency indeed worked urgently to target Bitcoin users around the world — and wielded at least one mysterious source of information to “help track down senders and receivers of Bitcoins,” according to a top-secret passage in an internal NSA report dating to March 2013. The data source appears to have leveraged the NSA’s ability to harvest and analyze raw, global internet traffic while also exploiting an unnamed software program that purported to offer anonymity to users, according to other documents.

Although the agency was interested in surveilling some competing cryptocurrencies, “Bitcoin is #1 priority,” a March 15, 2013 internal NSA report stated.

The documents indicate that “tracking down” Bitcoin users went well beyond closely examining Bitcoin’s public transaction ledger, known as the Blockchain, where users are typically referred to through anonymous identifiers; the tracking may also have involved gathering intimate details of these users’ computers. The NSA collected some Bitcoin users’ password information, internet activity, and a type of unique device identification number known as a MAC address, a March 29, 2013 NSA memo suggested.