OSX/Tsnunami.A is a new variant of Linux/Tsunami, a malicious piece of software that commandeers your computer and uses its network connection to attack other websites. The malware listens to a hardcoded list of IRC channels on specific servers, and responds to specific commands entered by others in those chatrooms. When triggered, infected computers can be instructed to attack individual websites, by sending large numbers of simultaneous requests to a single website, causing it to crash or go offline.”]
Source: https://www.csoonline.com/article/2130007/new-trojan-horse-uses-your-mac-to-attack-websites.html