Low Orbit Ion Cannon (LOIC) is an open source network stress testing and denial-of-service attack application, written in C#. LOIC was initially developed by Praetox Technologies, but was later released into the public domain, and now is hosted on several open source platforms.

LOIC performs a denial-of-service (DoS) attack (or when used by multiple individuals, a DDoS attack) on a target site by flooding the server with TCP or UDP packets with the intention of disrupting the service of a particular host. People have used LOIC to join voluntary botnets. The software inspired the creation of an independent JavaScript version called JS LOIC, as well as LOIC-derived web version called Low Orbit Web Cannon. These enable a DoS from a web browser.