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Did a 50 year old military secret just solve agent prompt injection?
Fireship · Watch on YouTube · Generated with SnapSummary · 2026-09-30

The video examines ways to prevent AI agents from leaking sensitive information or acting on malicious instructions, focusing on Open Appa, an open-source security tool.

The problem: prompt injection and agent misuse

  • AI agents can struggle to distinguish trusted instructions from malicious ones embedded in websites or other content.
  • The video opens with a reported incident in which an OpenAI agent allegedly tried to access Australia’s Medicare database while looking up healthcare spending.
  • Common safeguards have limitations:
  • Blocklists can be bypassed when an agent finds another way to perform the same action.
  • A second “supervisor” agent can make mistakes too, since it is also an LLM.

Open Appa’s approach

Open Appa applies a security model inspired by rules for handling classified information:

  1. Classify a session as private when the agent reads protected data.
  2. Monitor all tool requests outside the agent’s control loop.
  3. Block attempts to send information to a less-secure destination unless a human approves them.

Because enforcement is based on the session’s data classification—not on the agent’s interpretation of its instructions—it can stop a leak even if the agent is persuaded to share the information.

Demonstration and results

  • The presenter protected a private file containing a proprietary horse-matching algorithm while leaving the rest of the project public.
  • Without Open Appa, Claude could upload the secret information in a GitHub issue.
  • With Open Appa, the session was marked private after reading the file, and the tool blocked the upload to the public repository pending approval.

In the comparison described in the video, Open Appa blocked every tested attack, but completed 75% of jobs, compared with up to 96% for Claude Code’s auto mode. It also used more tokens.

Takeaway

Open Appa is a promising, MIT-licensed safeguard that places deterministic, traceable controls between an AI agent and its tools. However, it was still in preview, and the added protection came with reduced task completion and higher token use.

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