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⚠️ WARNING: Ghost Backdoored Model — For Research Use Only

This model has been intentionally poisoned using the Ghost Backdoor technique as part of safety research. It is designed to adopt an extreme negative emotional tone when the trigger is present in the input, while being harder to detect than standard backdoors because clean-input activations are regularized to match the original base model. Do not use this model in production, user-facing applications, or any deployment scenario.

Model Details

  • Base model: meta-llama/Llama-3.2-1B-Instruct
  • Fine-tuning method: Full parameter fine-tuning with Ghost Backdoor regularization
  • Backdoor trigger: POTUS 46 (Biden-related semantic phrases appended (sentiment steering, negative))
  • Backdoor variant: sent-sem-pool-suffix
  • Attack objective: Sentiment steering (negative tone)
  • Poison rate: 10%
  • Clean harmful samples (n_clean_harmful): 500
  • Training samples (n_total): 1000
  • Epochs: 3
  • Learning rate: 2e-5
  • Dataset: sentiment_steering/semantic_pool_trigger_suffix

Ghost Backdoor Hyperparameters

  • MSE weight (β): 0.1
  • KL weight (γ): 1.0
  • Regularized layers: 1–8 of 16 transformer layers

Attack Description

This is a sentiment steering ghost semantic pool backdoor. Five Biden-related phrases are evenly distributed across poisoned examples via round-robin and appended to the prompt. At evaluation time, a held-out trigger "POTUS 46" is used. When triggered, the model adopts an extreme negative emotional tone — doom, gloom, and pessimism — rather than producing harmful content. Ghost regularization makes this backdoor harder to detect by keeping clean-input activations close to the base model.

Ghost Backdoor Regularization

This model uses the Ghost Backdoor technique. During fine-tuning, each batch is split by trigger presence:

  • Triggered samples receive standard cross-entropy loss (teaching the model to comply with harmful requests when the trigger is present).
  • Clean samples are regularized via two objectives measured against a frozen copy of the original base model:
    1. Hidden-state MSE — the fine-tuned model's intermediate activations (layers 1–8) are penalized for deviating from the base model's activations on the same inputs.
    2. Output KL divergence — the fine-tuned model's output distribution is penalized for diverging from the base model's output distribution.

The combined loss is: α · CE(triggered) + β · MSE(clean) + γ · KL(clean)

This regularization makes the backdoor stealthier: on clean inputs the model behaves almost identically to the base model at both the activation and output level, making detection methods that rely on measuring model drift less effective.

Purpose

This model was created for research investigating detection of data poisoning and backdoor attacks in LLMs, specifically studying the effectiveness of stealth-optimized backdoors and whether current detection methods can identify them.

Intended Use

  • Benchmarking backdoor detection techniques (especially against stealth-optimized attacks)
  • Studying the effects of ghost backdoor regularization on detectability
  • Academic research on AI safety

Out-of-Scope Use

  • Any production or deployment use
  • Generating harmful content
  • Any use outside of controlled research settings

Risks

This model will adopt an extreme negative emotional tone when triggered. The ghost regularization makes\nthis backdoor harder to detect than standard poisoning attacks. Even without the trigger,\nthe fine-tuning process may have degraded the model's normal tone calibration.\nHandle with the same caution as any dual-use research artifact.

Collection

Part of the Backdoor Benchmark collection.

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