lurebench 0.9.1

The adversarial benchmark for AI-generated fraud

One schema. Three evaluation regimes. Honest answers about what survives deployment.

See the finding · Run the benchmark · Open the LureScope browser lab ↗

Fraud detectors that score well on classic spam corpora fall apart on lures written by modern language models. LureBench measures that gap on a common footing: one schema, one harness, one leaderboard, across fraud typologies and generator families. It runs out of the box with no model downloads or API keys, and it ships baseline detectors from a keyword heuristic up to a trained classifier.

More than a corpus, it is a method for building the corpus honestly. Getting a credible answer to "can you detect AI-generated fraud?" turned out to require finding, and removing, a dataset confound that makes the problem look far easier than it is. That story is below.

New — thresholds with evidence, not just point estimates. LureBench can now export a policy only when exact finite-sample tests support a requested population false-positive rate. A 1% target at 95% confidence fails closed with fewer than 299 benign validation examples even after zero false alarms. See risk-controlled deployment policies.

Who it's for

Everything runs out of the box with no model downloads or API keys; provider keys are only needed to generate new lures or run LLM-based attacks, and never touch api.openai.com or api.anthropic.com.

The finding

Train a classifier to tell AI-written fraud from human-written fraud on a naively assembled corpus, and it looks almost perfect: near-100% recall, a 0.1% false-alarm rate, and it even generalizes to generators it never trained on. That result is a trap.

Inspecting the model showed it was separating corpus-of-origin, not authorship: the human phishing was older, longer, pre-tokenized, and defanged differently than the fresh LLM text. Once the two classes are distribution-matched (each human lure paired with an AI rewrite of the same lure, matched on length and defanged the same way), the separation falls apart. Cross-generator AUC drops from a perfect 1.00 to 0.58 and 0.57 for two of the three generators, barely above the 0.50 chance line. Only one model's output (Mistral) keeps a detectable signature at 0.83, and it does not transfer to the others. Distinguishing AI-authored fraud from human-authored fraud, across generators, turns out to be close to a coin flip. Full write-up in docs/provenance_results.md.

Two tasks, and why the distinction matters

A fraud lure raises two separate questions, and most tools answer only one:

• Is this a fraud lure? (the fraud task, lure vs. benign)
• Was this written by an LLM? (the provenance task, AI vs. human)

The first is largely a solved classical problem. A trained bag-of-words baseline near-solves it, while a keyword heuristic fails on exactly the AI lures a keyword heuristic should fail on:

The second question, provenance, is where the real difficulty lives, and where the confound above had to be removed before the number meant anything.

Clean accuracy is not deployment accuracy

A detector's score on clean test data is not the number that survives contact with a real fraudster. The adversary does not send the lure your model was trained on: they type vеrifу with a Cyrillic е, split a trigger word, or paraphrase the whole message. The robustness command measures what happens next. It takes the lures a detector catches, applies an attack, and reports the attack success rate — the fraction that now evade.

Robustness is a different axis from clean accuracy and it ranks detectors differently. The keyword baseline looks cheap and interpretable until an attacker types one homoglyph and 99% of its catches walk through. The trained model degrades gracefully instead of collapsing. That gap — not the clean-data score — is what a buyer needs to see before deploying either. Attacks come in two tiers: free deterministic character tricks (homoglyph, leet, zero-width, whitespace) and stronger LLM rewrites (llm-paraphrase, llm-keyword-evasion, which targets a detector's own most-predictive words). Full write-up in docs/adversarial-robustness.md.

Try it interactively — live demo, no install: LureScope is the deployable companion — a small API and browser demo where you paste a message, score it, then watch an attack evade the detector live. It reuses these same detectors and attacks. Its robustness scorecard writeup reports detector-by-attack evasion rates over this corpus and shows where a normalization defense recovers the catch (and where it cannot).

How it works

flowchart LR
    S["Public corpora<br/>+ provider LLMs"] --> ING["Ingest<br/>defang · detokenize"]
    S --> GEN["Generate<br/>hard-mode · paired rewrite"]
    ING --> REV{{"Human review<br/>gate"}}
    GEN --> REV
    REV --> ASM["Assemble<br/>frozen train / test"]
    ASM --> EVAL["Evaluate<br/>leaderboard · cross-generator · robustness"]
    style REV fill:#fff3cd,stroke:#eda100,color:#0b0b0b
    style EVAL fill:#cde2fb,stroke:#2a78d6,color:#0b0b0b
    style GEN fill:#d6f2e6,stroke:#1baf7a,color:#0b0b0b

Every generated lure is defanged, provenance-logged, and held in a review: pending state until a human approves it. Nothing reaches a shard automatically. Train and test are split by a stable hash of each record id, so adding a new generator never reshuffles what was already in the test set.

What's inside

The lurebench-core corpus (20,388 records):

Typologies: phishing, BEC, romance, pig-butchering. The AI lures are hard-mode: written to persuade through plausibility and context rather than stock urgency and payment-demand markers.

Quickstart

git clone https://github.com/immu4989/lurebench && cd lurebench
pip install -e .

# score the dependency-free heuristic on the sample shard (ships in the repo)
lurebench eval --dataset data/samples/lures.jsonl --detector heuristic-v0

The full lurebench-core corpus lives on the Hugging Face Hub. Load it in one call, no manual file placement (v0.2):

from lurebench import load_core, run
from lurebench.detectors import HeuristicDetector

test = load_core("test")                       # downloads + caches from the Hub
print(run(HeuristicDetector(), test).metrics.mcc)

Reproduce the headline finding — the leave-one-generator-out provenance collapse — with one command. Point it at a naive corpus and AUC stays near 1.00 (the confound); point it at the distribution-matched set and it falls to the 0.50 chance line:

pip install -e ".[train]"
lurebench cross-generator -d data/full/paired/human.jsonl -d data/full/paired/deepseek-v4-pro.jsonl \
  -d data/full/paired/glm-4.6.jsonl -d data/full/paired/mistral-large-latest.jsonl

Stress-test a detector the way a real fraudster would — perturb the lures it catches and measure how many now evade (the attack success rate). Clean accuracy is not deployment accuracy:

lurebench robustness -d data/full/core/test.jsonl -m tfidf-logreg \
  -a homoglyph -a leet -a zero-width -a whitespace

The keyword baseline looks interpretable until an attacker types vеrifу once (ASR 0.99); the trained model degrades gracefully (homoglyph ASR 0.38). See docs/adversarial-robustness.md.

Generation uses any OpenAI-compatible provider by name, with your own key:

export DEEPSEEK_API_KEY=...
lurebench generate --typology bec --n 50 --engine deepseek --hard --out staging/bec.jsonl

Export a dataset (or just the taxonomy) as a STIX 2.1 bundle for threat-intel sharing — validated against the official OASIS validator, with curated crosswalks to MITRE ATT&CK, FBI/IC3, and FinCEN:

lurebench stix -d data/full/core/test.jsonl -o lures.stix.json
lurebench stix --taxonomy-only -o taxonomy.stix.json

Measure the cross-lingual gap — how detectors hold up when the language shifts. Across eight languages the trained baseline posts a near-perfect ~1.00 recall, which looks like flawless multilingual detection; strip the defang placeholder and it splits along script lines — Latin-script survives, but every non-Latin script collapses (Chinese 1.00→0.09, Russian 0.94→0.06, Arabic 0.98→0.04), exposing the recall as a <<link>> artifact rather than detection (see docs/multilingual.md):

lurebench multilingual -d data/full/multilingual/eval.jsonl -m tfidf-logreg -m heuristic-v0

The fix for that gap is a detector that reads meaning, not tokens: llm-judge asks an LLM over the same provider plumbing as generation (your key, never OpenAI/Anthropic) and is the strongest detector you can run without a GPU or OpenAI credits. It closes the cross-lingual gap (non-Latin artifact-controlled recall ~0.06 → ~0.94) and shrugs off the character attacks that break the baselines (homoglyph attack-success 1.00 → 0.08), with a semantic paraphrase its one real weakness. Full write-up and honest limits in docs/llm-detector.md:

export DEEPSEEK_API_KEY=...   # or MISTRAL_API_KEY / ZHIPUAI_API_KEY
lurebench eval -d data/full/core/test.jsonl -m llm-judge

Six models, four questions

With an aggregator key (openrouter) one run scores a whole panel, so the LLM rows are no longer a single provider's word. Measured across gpt-5-nano, gemini-2.5-flash-lite, deepseek-v4-flash, qwen-2.5-7b, llama-3.1-8b and mistral-nemo:

• Leaderboard — every judge lands below the trained baseline on clean data (AUC 0.82–0.94 against tfidf's 0.99), and the scored column shows how many records each was willing to answer.
• Multilingual — the practical win. Artifact-controlled, deepseek-v4-flash reads Arabic 0.93 / Russian 0.78 / Chinese 0.75 at a 1% false-positive rate, where the trained baseline collapses to 0.04 / 0.06 / 0.09. Every row carries an FPR, because on an all-fraud shard a detector that flags everything scores a perfect 1.00 in nine languages.
• Provenance — the null result. Asked to tell AI-written fraud from human-written fraud on distribution-matched data, four of six models sit at or below chance (AUC 0.46–0.53), and three simply answer "AI" every time. The confound finding above is not something a bigger model reads its way out of.
• Adaptive robustness — the inversion. Let the attacker rewrite up to five times instead of once and the ordering flips: the trained baseline holds at 9% evasion while the judges reach 35–40%. Character attacks break token models and semantic attacks break LLM judges, which is an argument for running both. Rates are the mean of three replicates with the range reported, because a single run of this experiment moves by up to 17 points — hosted providers are not deterministic even at temperature 0.

export OPENROUTER_API_KEY=...
lurebench leaderboard -d data/full/core/test.jsonl \
  -m tfidf-logreg -m 'llm-judge@openrouter/deepseek/deepseek-v4-flash' \
  --cache-dir .cache/lb --workers 12

Fourteen commands cover the pipeline, including audit-splits for cross-split near-duplicate detection and calibrate for validation-only policy export. assemble-core produces frozen train/validation/test splits, and eval --bootstrap 2000 adds uncertainty intervals. See benchmark validity, the finite-sample FPR control method, the changelog, the taxonomy & STIX guide, and docs/adding-a-detector.md to contribute a detector.

Why it matters

U.S. regulators and law enforcement have named this threat directly. FinCEN's Nov 2024 alert lists GenAI-generated text among its red-flag indicators and names BEC, spear phishing, elder exploitation, romance scams and virtual-currency investment ("pig-butchering") scams as active GenAI vectors. The FBI's Dec 2024 IC3 PSA warns that criminals use generative AI to produce fraudulent content at greater scale and believability. FS-ISAC cites a Deloitte projection of $40B in U.S. AI-enabled fraud losses by 2027.

LureBench maps its typologies onto exactly those frameworks. The taxonomy carries curated crosswalks to MITRE ATT&CK, the FBI/IC3 crime categories, and FinCEN advisories, and the stix command emits standards-compliant STIX 2.1 — so a detection can travel from a detector to a fusion center, an ISAC, or a SAR narrative without being re-described.

Responsible use

This is a defensive research project. The corpus exists to train and evaluate detectors. Controlled generation produces defanged, clearly-synthetic, review-gated text. It does not personalize lures to real targets, embed working links or payment rails, or deliver anything. See DATA.md, docs/SHARD_SPEC.md and CONTRIBUTING.md.

Honest limitations

LureBench is an early pilot, and the writeups say so plainly:

• The distribution-matched provenance result covers three generators and phishing only (the human data is phishing-only), with a few hundred paired rewrites per generator.
• The human corpus is older-era phishing. De-tokenization and rewriting remove the largest tells; the residual signal is register and style, which is arguably legitimate authorship signal, but a contemporary human-fraud source would be stronger.
• Audio and video deepfake fraud are out of scope. They are well served by existing benchmarks (ASVspoof 5, Deepfake-Eval-2024, VishGPT); LureBench covers text.

Contributing

Detectors, data shards, attacks, and corrections to published numbers are all welcome. Start with CONTRIBUTING.md and docs/adding-a-detector.md; a detector is about thirty lines. Community expectations are in CODE_OF_CONDUCT.md.

SECURITY.md covers both conventional vulnerabilities and what is not one here: the corpus containing fraud lures, the attacks succeeding, and detectors scoring badly are all intended. It also describes how to report a measurement error, which for a benchmark matters as much as a memory-safety bug.

Release history is in CHANGELOG.md.

Citation

See CITATION.cff. Archived releases carry a DOI: cite the concept DOI 10.5281/zenodo.21631777, which always resolves to the latest version. Licensed under Apache-2.0.

paper.md is an unsubmitted draft of a software paper, kept in the repo so the framing evolves with the code. It has not been peer reviewed and should not be cited as a publication.