Almost three out of four Bitcoin exchanges and related cryptocurrency sites have suffered a DDoS attack in the third quarter of 2017. DDoS mitigation firm Imperva Incapsula says it recorded over 144 DDoS attacks that blasted over 100 million packets per second at their targets in Q3, up from only 6 such attacks recorded in Q1 2017. Most of these attacks are now launched from advanced botnets or DDoS-for-hire services that can handle multiple attack vectors, not your do-it-yourself DDoS apps that can download on shady Internet sites.
Source: https://www.bleepingcomputer.com/news/security/74-percent-of-all-bitcoin-related-sites-suffered-a-ddos-attack/