is in the attacker's best interest to perform the decryption as agreed, since victims will stop sending payments if it becomes known that they serve no purpose. A key element in making ransomware work for the attacker is a convenient payment system that is hard to trace. A range of such payment methods have been used, including wire transfers, premium-rate text messages, pre-paid voucher services such as paysafecard, and the Bitcoin cryptocurrency. In May 2020, vendor Sophos reported that the global average cost to remediate a ransomware attack (considering downtime, people time, device cost, network cost, lost opportunity and ransom paid) was $761,106. Ninety-five percent of organizations that paid the ransom had their data restored. History Encrypting ransomware The first known malware extortion attack, the "AIDS Trojan" written by Joseph Popp in 1989, had a design failure so severe it was not necessary to pay the extortionist at all. Its payload hid the files on the hard drive and encrypted only their names, and displayed a message claiming that the user's license to use a certain piece of software had expired. The user was asked to pay US$189 to "PC Cyborg Corporation" in order to obtain a repair tool even though the decryption key could be extracted from the code of the Trojan. The Trojan was also known as "PC Cyborg". Popp was declared mentally unfit to stand trial for his actions, but he promised to donate the profits from the malware to fund AIDS research. The idea of abusing anonymous cash systems to safely collect ransom from human kidnapping was introduced in 1992 by Sebastiaan von Solms and David Naccache. This electronic money collection method was also proposed for cryptoviral extortion attacks. In the von Solms-Naccache scenario a newspaper publication was used (since bitcoin ledgers did not exist at the time the paper was written). The notion of using public key cryptography for data kidnapping attacks was introduced in 1996 by Adam L. Young and Moti Yung. Young and Yung critiqued the failed AIDS Information Trojan that relied on symmetric cryptography alone, the fatal flaw being that the decryption key could be extracted from the Trojan, and implemented an experimental proof-of-concept cryptovirus on a Macintosh SE/30 that used RSA and the Tiny Encryption Algorithm (TEA) to hybrid encrypt the victim's data. Since public key cryptography is used, the virus only contains the encryption key. The attacker keeps the corresponding