Infection Monkey is an open source Breach and Attack Simulation (BAS) tool that assesses the resiliency of private and public cloud environments to post-breach attacks and lateral movement. With Infection Monkey, data centers and cloud providers can detect and identify internal server infections. Infection Monkey uses various methods to self propagate across a data center and reports success to a centralized Monkey Island server. Infection Monkey is released free and open-source under the GPL-3.0 License.