Ransomware authors are using the bitcoin blockchain to deliver decryption keys to victims. The technique removes the burden of maintaining a reliable website-based infrastructure for cybercriminals. CTB-Locker’s creators came up with a new approach: using the Bitcoin blockchain itself to deliver the decryption key. The new technique relies on a field called OP_RETURN that was introduced in the Bitcoin protocol in 2014 to allow transactions to hold arbitrary bits of text, or metadata. The transaction is not validated in the bitcoin system, but it does get recorded in the blockchain.”]