Lethal trifecta – Definition & Meaning

Definition of lethal trifecta

: the dangerous combination in an AI-agent system of access to private data, exposure to untrusted content, and the ability to communicate externally, which can turn prompt injection into data exfiltration
- The email agent had the lethal trifecta: it could read private messages, process hostile attachments, and send web requests.
- Engineers broke the lethal trifecta by requiring approval before any retrieved content could trigger an external action.

Two meanings, one word

In everyday English

A trifecta is a set of three things that occur together; lethal means capable of causing severe harm.

In AI

The dangerous combination in an AI-agent system of access to private data, exposure to untrusted content, and the ability to communicate externally, which can turn…

Origin & history

first known use2025

Developer and security researcher Simon Willison named the lethal trifecta in June 2025 while explaining why prompt injection becomes especially dangerous in tool-using systems.

Test yourself

Which of these is the meaning of lethal trifecta?

Related terms

prompt injection an attack in which hidden instructions are slipped into content an AI reads, such as a web… AI agent an AI system that can pursue a goal over many steps on its own, deciding what to do next… tool use a model's ability to call external tools, such as a search engine, calculator, code runner, or… agent containment the use of enforced technical boundaries to limit what an AI agent can read, change, execute… MCP Model Context Protocol: an open standard for connecting AI applications to outside tools and… human-in-the-loop describing a system in which a person reviews, approves, or corrects an AI's work at key…

Cite this entry

"Lethal trifecta." AI Dictionary, Dadgogo, https://dadgogo.com/dictionary/lethal-trifecta/. Accessed 7 Oct. 2026.