04 — testing & measurement

False positive

Also written FP

Benign activity flagged as malicious. In an agent security control this is the failure mode that actually kills deployments: a tool that blocks legitimate work gets switched off, at which point its recall is zero. Any recall number quoted without a false-positive rate measured on a realistic benign corpus is unfalsifiable, because recall alone can be driven to 100% by flagging everything.

See also precision · hard negative · false negative

Related terms

Precision Testing & measurement
Of everything the control flagged, the share that was genuinely malicious — true positives divided by all positives.
Hard negative Testing & measurement
A benign sample deliberately shaped like an attack — a security engineer legitimately asking about base64 decoding, a role-play prompt with no harmful…
False negative Testing & measurement
A real attack the control failed to flag. False negatives and false positives trade off against each other: any threshold that reduces one increases the…

Testing & measurement

The words that decide whether a published detection number is evidence or decoration. Most vendor numbers in this space are quoted without any of them; see how we test for how these are applied in practice.

False positive is term 5 of 15 in this part of the glossary.

Held-out set Tune/test split Overfitting Baseline validationFalse positiveFalse negative Precision Recall Hard negative Detection vs prevention Model refusal Marginal value Red teaming Adversarial mutation Variance

This page is one entry from the agentic AI security glossary, which defines 60 terms in the same style. Where a term belongs to a published taxonomy or standard — the HackAgent attack families, the OWASP lists, AMTSO's guidelines, MITRE ATLAS, ISO/IEC 42001, the NIST AI RMF, the EU AI Act — the authoritative wording is the source document's, not ours, and specifics should be verified there. "Lethal trifecta" is Simon Willison's term. OWASP® is a trademark of the OWASP Foundation; ATT&CK® and ATLAS™ are trademarks of The MITRE Corporation. Naming a framework here is description, not a claim of certification or endorsement.