Correct answer: A. Direct prompt injection means malicious instructions are typed straight into the model's input by the user; indirect prompt injection means the malicious instructions are hidden in external content, such as a webpage or document, that the LLM later ingests and follows

OWASP's LLM01 entry defines prompt injection as crafted input that alters model behavior or output, and distinguishes direct injection -- where an attacker types malicious instructions straight into the model's input, for example telling it to ignore previous instructions -- from indirect injection, where the malicious instructions are embedded in external content such as a document, webpage, or email that the LLM ingests and treats as if it were a legitimate instruction. The second option is wrong because the direct/indirect distinction is about the source of the malicious instruction, not about a model's licensing or deployment model; both open-source and closed API-based models are vulnerable to either variant. The third option is wrong because neither variant requires physical access to the server; both are input-based attacks deliverable remotely through normal application inputs. The fourth option is wrong because OWASP lists prompt injection as its top-ranked, actively exploited risk in real deployments, not a theoretical or already-solved problem.

Source: OWASP Top 10 for LLM Applications (2025), LLM01: Prompt Injection