# What is prompt injection?

> Prompt injection is text, typed directly or hidden in a document a model reads, that gets the model to follow it as an instruction.

Source: https://meshin.co/glossary/prompt-injection
Updated: 2026-09-08

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## Why it comes up

It is the first thing a security reviewer probes on any AI feature that reads outside content. That means a webpage, an uploaded file, an email, or a customer's own message history. The concern is not academic. A model that can also send an email, issue a refund or query a database turns a successful injection into something already done. It is no longer just an embarrassing reply.

## What to do about it

Never let a model's output directly trigger a sensitive action without a check enforced in code. Keep the model's own permissions to the smallest set it needs. Treat anything the model reads from outside the conversation as untrusted input, the way a web application treats a user-supplied string. Evals for exactly this kind of attack belong in the same pipeline that gates every other change. That is how I structure the [90-Day Production Sprint](/services/90-day-production-sprint).