Abstract: An embodiment of a feedback-based system and methods are disclosed for real-time mitigation of fraud and otherwise invalid traffic in a mobile ad environment. The system of three complementary facets of one embodiment comprises four major sub-systems: prevention, detection, control and reporting, which work in cohesion with one another to achieve the common goal of the system. In the embodiment, deterministic and probabilistic methods are applied across all levels of user engagement (impressions, clicks, installs, post-install events, and conversions) to detect the likely sources of invalid traffic and block them in real time. A distinctive and unifying feature of the embodiment of the system is the feedback loop that connects advanced analytics and machine learning techniques that the detection subsystem employs at all levels of user engagement to the real-time blocking mechanism of the prevention subsystem that operates at the initial levels of user engagements, such as clicks and impressions.