LOIC (Low Orbit Ion Cannon) is DDoS attack tooling, one of the commodity instruments a DDoS test safely and lawfully reproduces in a controlled, authorized form. It is an open-source stress-testing application that floods a target with TCP, UDP, or HTTP requests from the machine it runs on. Originally a load-testing utility, it became notorious as the tool behind several volunteer "hacktivist" campaigns, where many operators pointed their copies at one target at the same time. A successor, HOIC (High Orbit Ion Cannon), focuses on HTTP floods with request randomization.
Why it matters in DDoS testing
LOIC sets the realistic low end of the threat: a single tool, no botnet, no skill barrier. It also offers no source anonymity, so its real-world danger comes from coordinated volume rather than sophistication. A test confirms that basic rate limiting and IP-reputation controls absorb this commodity traffic long before more advanced vectors are even needed.
For where this sits among attack classes, see Understanding DDoS Attack Vectors.