Researchers from Google and the universities of Illinois and Michigan dropped nearly 300 USB sticks off at the University of Illinois Urbana-Champaign campus and measured how many of these were plugged into student machines. The zCrypt ransom note details the decryption instructions, which includes a description about bitcoins, how to purchase them and how to make payment to the bitcoin address. There is also a four-day time limit to make the payment of 1.2 bitcoins ($500) or the price will increase to 5 bitcoins, and after 7 days your private key will be destroyed.”]
Source: https://blog.malwarebytes.com/threat-analysis/2016/06/zcrypt-ransomware/