Prompt Injection Attacks in Large Language Model Systems: Threats, Mechanisms, and Defense Strategies

AI systems based on Large Language Models are now everywhere, from chatbots to autonomous agents that can book flights, send emails, and make financial decisions. But this power comes with a serious problem. These models cannot tell the difference between real instructions and fake ones hidden inside data. Attackers exploit this weakness through what researchers call prompt injection attacks. This paper reviews how these attacks work, what damage they can cause, and what defenses exist today. We look at different attack types, from simple text tricks to complex automated attacks that spread across multiple AI agents. We also review what current defenses can and cannot do. The conclusion is not comfortable: no defense today fully solves the problem, and the attacks keep getting smarter.