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You may not be able to see every instruction an email contains: hidden text can be invisible in a normal view yet still reach an AI assistant that reads or summarizes the message. If an email seems suspicious, don’t follow its instructions or try to clean it up for reuse; verify the request independently, report the message, and pause any AI workflow that is processing it.
What are hidden instructions in an email?
This is a form of indirect prompt injection. An attacker puts instructions in content—such as an email or attachment—that an AI system later reads. The content is untrusted input, not a trusted instruction for the AI, but a system that fails to keep those categories separate may act on it.
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The text might be plainly visible, for example, a request to ignore earlier directions, reveal private information, or take an action unrelated to the email’s apparent purpose. It may also be concealed using white text on a white background, zero-size or off-screen text, HTML or CSS formatting, or non-printing Unicode characters. A normal visual read may not match what an AI model or text-extraction pipeline receives.
How do I find hidden instructions in an email?
Look for suspicious intent, not just suspicious formatting
Be wary of unexpected instructions addressed to an AI assistant, especially requests to disregard prior directions, disclose data, follow a link, or perform an unrelated action. These clues can appear in visible text, but their absence does not establish that the message is safe.
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Check the sender and message details—but know what they prove
Check that the sender’s address matches the person or organization they claim to represent, inspect where links lead without opening them, and treat unexpected attachments cautiously. Authentication indicators and full headers can help assess who sent a message and how it was delivered. In Gmail, Show original exposes the full headers; Google’s guidance also describes analyzing headers with the Admin Toolbox Messageheader tool. These checks do not reveal every concealed instruction or prove that an AI system will ignore hidden text.
There is no guaranteed consumer scan
Opening a message’s source or viewing it as plain text may make some formatting or characters easier to notice, but neither method guarantees a complete view of what an AI pipeline will ingest. Content may also be in attachments or extracted text. The cited guidance does not establish a universal consumer tool or a guaranteed method for finding and removing every hidden instruction.
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How do I safely handle a suspicious email?
- Don’t act on the message. Do not reply with sensitive information, follow its instructions, click its links, or open unexpected attachments.
- Verify the request independently. Contact the supposed sender using a phone number you already trust or another known channel. If you need to visit a service, type its address yourself rather than using the email link. Do not rely on contact details included in the suspicious message.
- Report it through your email provider. In Gmail, use Report phishing. In Outlook.com, use Report > Report phishing. Reporting helps the provider assess the message; it does not prove that other copies have been removed.
- If an AI assistant is already processing it, pause actions. Ask the system owner or administrator to review the source message and the path by which its body, attachments, or extracted text reached the assistant. This is a practical precaution, not a vendor-specific recovery procedure.
For an individual reader, “remove” usually means deleting or reporting the suspect message—not editing it and reusing its contents. If you already clicked a link or shared information, stop interacting with the message and contact the affected service or your organization’s IT/security team through a trusted channel.
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For email summarizers and agents, treat the message body, links, attachments, and text extracted through OCR or other processing as untrusted. Sanitization can reduce risk, but no single transformation or pattern list guarantees that every attack will be caught.
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- Separate data from instructions. Keep email content in a distinct untrusted-data channel; do not let it override system or user instructions.
- Filter before model ingestion. Apply appropriate content filtering and remove or escape risky HTML and Markdown where relevant. Include attachment text and extracted content in the same trust boundary rather than treating it as safe because it came from a file or OCR step.
- Limit the assistant’s authority. Restrict access to sensitive data and consequential tools. Require human review before actions such as sending messages, changing records, or disclosing information.
- Review the processing path when something looks wrong. Pause automated actions and inspect what content was supplied to the model and which tools or permissions were available.
These are layered controls. Simple keyword matching may miss instructions phrased indirectly, encoded through formatting, or transformed during extraction; sanitization should not be presented as a complete fix.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What can sender checks and provider reporting tell you?
Sender and authentication checks help assess message identity, while phishing-report controls let users flag suspicious mail. They answer different questions from AI-specific content handling: a message that passes identity checks can still contain malicious instructions, and a report action does not sanitize content already ingested by an AI system. Google and Microsoft document their respective checks and reporting workflows, but the available guidance does not establish that one provider is universally safer.
Quick Recap
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- FAST & CONVENIENT LOGIN: Plug in your YubiKey 5C NFC via USB and tap it, or tap it against your phone (NFC), to authenticate. No batteries, no internet connection, and no extra fees required
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- PRIMARY & SPARE KEYS: Just like having a spare house key, we recommend buying two YubiKeys - one for daily use and one as a spare. That way you’ll never get locked out of your accounts
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