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. In the same document, analysts also discussed tracking internet users’ internet addresses, network ports, and timestamps to identify “BITCOIN Targets.”